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| <section id="tabular-datasets"> |
| <span id="cpp-dataset"></span><h1>Tabular Datasets<a class="headerlink" href="#tabular-datasets" title="Permalink to this heading">#</a></h1> |
| <div class="admonition seealso"> |
| <p class="admonition-title">See also</p> |
| <p><a class="reference internal" href="api/dataset.html"><span class="doc">Dataset API reference</span></a></p> |
| </div> |
| <div class="admonition warning"> |
| <p class="admonition-title">Warning</p> |
| <p>The <code class="docutils literal notranslate"><span class="pre">arrow::dataset</span></code> namespace is experimental, and a stable API |
| is not yet guaranteed.</p> |
| </div> |
| <p>The Arrow Datasets library provides functionality to efficiently work with |
| tabular, potentially larger than memory, and multi-file datasets. This includes:</p> |
| <ul class="simple"> |
| <li><p>A unified interface that supports different sources and file formats and |
| different file systems (local, cloud).</p></li> |
| <li><p>Discovery of sources (crawling directories, handling partitioned datasets with |
| various partitioning schemes, basic schema normalization, …)</p></li> |
| <li><p>Optimized reading with predicate pushdown (filtering rows), projection |
| (selecting and deriving columns), and optionally parallel reading.</p></li> |
| </ul> |
| <p>The supported file formats currently are Parquet, Feather / Arrow IPC, CSV and |
| ORC (note that ORC datasets can currently only be read and not yet written). |
| The goal is to expand support to other file formats and data sources |
| (e.g. database connections) in the future.</p> |
| <section id="reading-datasets"> |
| <span id="cpp-dataset-reading"></span><h2>Reading Datasets<a class="headerlink" href="#reading-datasets" title="Permalink to this heading">#</a></h2> |
| <p>For the examples below, let’s create a small dataset consisting |
| of a directory with two parquet files:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos">49</span><span class="c1">// Generate some data for the rest of this example.</span> |
| <span class="linenos">50</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">>></span><span class="w"> </span><span class="n">CreateTable</span><span class="p">()</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">51</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">schema</span><span class="w"> </span><span class="o">=</span> |
| <span class="linenos">52</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">schema</span><span class="p">({</span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">int64</span><span class="p">()),</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"b"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">int64</span><span class="p">()),</span> |
| <span class="linenos">53</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"c"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">int64</span><span class="p">())});</span> |
| <span class="linenos">54</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Array</span><span class="o">></span><span class="w"> </span><span class="n">array_a</span><span class="p">;</span> |
| <span class="linenos">55</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Array</span><span class="o">></span><span class="w"> </span><span class="n">array_b</span><span class="p">;</span> |
| <span class="linenos">56</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Array</span><span class="o">></span><span class="w"> </span><span class="n">array_c</span><span class="p">;</span> |
| <span class="linenos">57</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">NumericBuilder</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Int64Type</span><span class="o">></span><span class="w"> </span><span class="n">builder</span><span class="p">;</span> |
| <span class="linenos">58</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">({</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">9</span><span class="p">}));</span> |
| <span class="linenos">59</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">(</span><span class="o">&</span><span class="n">array_a</span><span class="p">));</span> |
| <span class="linenos">60</span><span class="w"> </span><span class="n">builder</span><span class="p">.</span><span class="n">Reset</span><span class="p">();</span> |
| <span class="linenos">61</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">({</span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">}));</span> |
| <span class="linenos">62</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">(</span><span class="o">&</span><span class="n">array_b</span><span class="p">));</span> |
| <span class="linenos">63</span><span class="w"> </span><span class="n">builder</span><span class="p">.</span><span class="n">Reset</span><span class="p">();</span> |
| <span class="linenos">64</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">({</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">}));</span> |
| <span class="linenos">65</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">(</span><span class="o">&</span><span class="n">array_c</span><span class="p">));</span> |
| <span class="linenos">66</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span><span class="n">schema</span><span class="p">,</span><span class="w"> </span><span class="p">{</span><span class="n">array_a</span><span class="p">,</span><span class="w"> </span><span class="n">array_b</span><span class="p">,</span><span class="w"> </span><span class="n">array_c</span><span class="p">});</span> |
| <span class="linenos">67</span><span class="p">}</span> |
| <span class="linenos">68</span> |
| <span class="linenos">69</span><span class="c1">// Set up a dataset by writing two Parquet files.</span> |
| <span class="linenos">70</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span><span class="w"> </span><span class="n">CreateExampleParquetDataset</span><span class="p">(</span> |
| <span class="linenos">71</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">root_path</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">72</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">base_path</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">root_path</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">"/parquet_dataset"</span><span class="p">;</span> |
| <span class="linenos">73</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">filesystem</span><span class="o">-></span><span class="n">CreateDir</span><span class="p">(</span><span class="n">base_path</span><span class="p">));</span> |
| <span class="linenos">74</span><span class="w"> </span><span class="c1">// Create an Arrow Table</span> |
| <span class="linenos">75</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">table</span><span class="p">,</span><span class="w"> </span><span class="n">CreateTable</span><span class="p">());</span> |
| <span class="linenos">76</span><span class="w"> </span><span class="c1">// Write it into two Parquet files</span> |
| <span class="linenos">77</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">output</span><span class="p">,</span> |
| <span class="linenos">78</span><span class="w"> </span><span class="n">filesystem</span><span class="o">-></span><span class="n">OpenOutputStream</span><span class="p">(</span><span class="n">base_path</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">"/data1.parquet"</span><span class="p">));</span> |
| <span class="linenos">79</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">parquet</span><span class="o">::</span><span class="n">arrow</span><span class="o">::</span><span class="n">WriteTable</span><span class="p">(</span> |
| <span class="linenos">80</span><span class="w"> </span><span class="o">*</span><span class="n">table</span><span class="o">-></span><span class="n">Slice</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">),</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">default_memory_pool</span><span class="p">(),</span><span class="w"> </span><span class="n">output</span><span class="p">,</span><span class="w"> </span><span class="cm">/*chunk_size=*/</span><span class="mi">2048</span><span class="p">));</span> |
| <span class="linenos">81</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">output</span><span class="p">,</span> |
| <span class="linenos">82</span><span class="w"> </span><span class="n">filesystem</span><span class="o">-></span><span class="n">OpenOutputStream</span><span class="p">(</span><span class="n">base_path</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">"/data2.parquet"</span><span class="p">));</span> |
| <span class="linenos">83</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">parquet</span><span class="o">::</span><span class="n">arrow</span><span class="o">::</span><span class="n">WriteTable</span><span class="p">(</span> |
| <span class="linenos">84</span><span class="w"> </span><span class="o">*</span><span class="n">table</span><span class="o">-></span><span class="n">Slice</span><span class="p">(</span><span class="mi">5</span><span class="p">),</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">default_memory_pool</span><span class="p">(),</span><span class="w"> </span><span class="n">output</span><span class="p">,</span><span class="w"> </span><span class="cm">/*chunk_size=*/</span><span class="mi">2048</span><span class="p">));</span> |
| <span class="linenos">85</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">base_path</span><span class="p">;</span> |
| <span class="linenos">86</span><span class="p">}</span> |
| </pre></div> |
| </div> |
| <p>(See the full example at bottom: <a class="reference internal" href="#cpp-dataset-full-example"><span class="std std-ref">A note on transactions & ACID guarantees</span></a>.)</p> |
| <section id="dataset-discovery"> |
| <h3>Dataset discovery<a class="headerlink" href="#dataset-discovery" title="Permalink to this heading">#</a></h3> |
| <p>A <a class="reference internal" href="api/dataset.html#_CPPv4N5arrow7dataset7DatasetE" title="arrow::dataset::Dataset"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::dataset::Dataset</span></code></a> object can be created using the various |
| <a class="reference internal" href="api/dataset.html#_CPPv4N5arrow7dataset14DatasetFactoryE" title="arrow::dataset::DatasetFactory"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::dataset::DatasetFactory</span></code></a> objects. Here, we’ll use the |
| <a class="reference internal" href="api/dataset.html#_CPPv4N5arrow7dataset24FileSystemDatasetFactoryE" title="arrow::dataset::FileSystemDatasetFactory"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::dataset::FileSystemDatasetFactory</span></code></a>, which can create a dataset |
| given a base directory path:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos">162</span><span class="c1">// Read the whole dataset with the given format, without partitioning.</span> |
| <span class="linenos">163</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">>></span><span class="w"> </span><span class="n">ScanWholeDataset</span><span class="p">(</span> |
| <span class="linenos">164</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span> |
| <span class="linenos">165</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">FileFormat</span><span class="o">>&</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">base_dir</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">166</span><span class="w"> </span><span class="c1">// Create a dataset by scanning the filesystem for files</span> |
| <span class="hll"><span class="linenos">167</span><span class="w"> </span><span class="n">fs</span><span class="o">::</span><span class="n">FileSelector</span><span class="w"> </span><span class="n">selector</span><span class="p">;</span> |
| </span><span class="hll"><span class="linenos">168</span><span class="w"> </span><span class="n">selector</span><span class="p">.</span><span class="n">base_dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">base_dir</span><span class="p">;</span> |
| </span><span class="hll"><span class="linenos">169</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span> |
| </span><span class="hll"><span class="linenos">170</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">factory</span><span class="p">,</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDatasetFactory</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="n">selector</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span> |
| </span><span class="hll"><span class="linenos">171</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemFactoryOptions</span><span class="p">()));</span> |
| </span><span class="hll"><span class="linenos">172</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">dataset</span><span class="p">,</span><span class="w"> </span><span class="n">factory</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| </span><span class="linenos">173</span><span class="w"> </span><span class="c1">// Print out the fragments</span> |
| <span class="linenos">174</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">fragments</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">GetFragments</span><span class="p">())</span> |
| <span class="linenos">175</span><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="k">auto</span><span class="o">&</span><span class="w"> </span><span class="n">fragment</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">fragments</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">176</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"Found fragment: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">fragment</span><span class="p">)</span><span class="o">-></span><span class="n">ToString</span><span class="p">()</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> |
| <span class="linenos">177</span><span class="w"> </span><span class="p">}</span> |
| <span class="linenos">178</span><span class="w"> </span><span class="c1">// Read the entire dataset as a Table</span> |
| <span class="linenos">179</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scan_builder</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">NewScan</span><span class="p">());</span> |
| <span class="linenos">180</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner</span><span class="p">,</span><span class="w"> </span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">181</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">scanner</span><span class="o">-></span><span class="n">ToTable</span><span class="p">();</span> |
| <span class="linenos">182</span><span class="p">}</span> |
| </pre></div> |
| </div> |
| <p>We’re also passing the filesystem to use and the file format to use for reading. |
| This lets us choose between (for example) reading local files or files in Amazon |
| S3, or between Parquet and CSV.</p> |
| <p>In addition to searching a base directory, we can list file paths manually.</p> |
| <p>Creating a <a class="reference internal" href="api/dataset.html#_CPPv4N5arrow7dataset7DatasetE" title="arrow::dataset::Dataset"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::dataset::Dataset</span></code></a> does not begin reading the data |
| itself. It only crawls the directory to find all the files (if needed), which can |
| be retrieved with <a class="reference internal" href="api/dataset.html#_CPPv4NK5arrow7dataset17FileSystemDataset5filesEv" title="arrow::dataset::FileSystemDataset::files"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">arrow::dataset::FileSystemDataset::files()</span></code></a>:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="c1">// Print out the files crawled (only for FileSystemDataset)</span> |
| <span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="k">auto</span><span class="o">&</span><span class="w"> </span><span class="n">filename</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">files</span><span class="p">())</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">filename</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> |
| <span class="p">}</span> |
| </pre></div> |
| </div> |
| <p>…and infers the dataset’s schema (by default from the first file):</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">schema</span><span class="p">()</span><span class="o">-></span><span class="n">ToString</span><span class="p">()</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> |
| </pre></div> |
| </div> |
| <p>Using the <a class="reference internal" href="api/dataset.html#_CPPv4N5arrow7dataset7Dataset7NewScanEv" title="arrow::dataset::Dataset::NewScan"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">arrow::dataset::Dataset::NewScan()</span></code></a> method, we can build a |
| <a class="reference internal" href="api/dataset.html#_CPPv4N5arrow7dataset7ScannerE" title="arrow::dataset::Scanner"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::dataset::Scanner</span></code></a> and read the dataset (or a portion of it) into |
| a <a class="reference internal" href="api/table.html#_CPPv4N5arrow5TableE" title="arrow::Table"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::Table</span></code></a> with the <a class="reference internal" href="api/dataset.html#_CPPv4N5arrow7dataset7Scanner7ToTableEv" title="arrow::dataset::Scanner::ToTable"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">arrow::dataset::Scanner::ToTable()</span></code></a> |
| method:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos">162</span><span class="c1">// Read the whole dataset with the given format, without partitioning.</span> |
| <span class="linenos">163</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">>></span><span class="w"> </span><span class="n">ScanWholeDataset</span><span class="p">(</span> |
| <span class="linenos">164</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span> |
| <span class="linenos">165</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">FileFormat</span><span class="o">>&</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">base_dir</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">166</span><span class="w"> </span><span class="c1">// Create a dataset by scanning the filesystem for files</span> |
| <span class="linenos">167</span><span class="w"> </span><span class="n">fs</span><span class="o">::</span><span class="n">FileSelector</span><span class="w"> </span><span class="n">selector</span><span class="p">;</span> |
| <span class="linenos">168</span><span class="w"> </span><span class="n">selector</span><span class="p">.</span><span class="n">base_dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">base_dir</span><span class="p">;</span> |
| <span class="linenos">169</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span> |
| <span class="linenos">170</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">factory</span><span class="p">,</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDatasetFactory</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="n">selector</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span> |
| <span class="linenos">171</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemFactoryOptions</span><span class="p">()));</span> |
| <span class="linenos">172</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">dataset</span><span class="p">,</span><span class="w"> </span><span class="n">factory</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">173</span><span class="w"> </span><span class="c1">// Print out the fragments</span> |
| <span class="linenos">174</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">fragments</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">GetFragments</span><span class="p">())</span> |
| <span class="linenos">175</span><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="k">auto</span><span class="o">&</span><span class="w"> </span><span class="n">fragment</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">fragments</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">176</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"Found fragment: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">fragment</span><span class="p">)</span><span class="o">-></span><span class="n">ToString</span><span class="p">()</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> |
| <span class="hll"><span class="linenos">177</span><span class="w"> </span><span class="p">}</span> |
| </span><span class="hll"><span class="linenos">178</span><span class="w"> </span><span class="c1">// Read the entire dataset as a Table</span> |
| </span><span class="hll"><span class="linenos">179</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scan_builder</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">NewScan</span><span class="p">());</span> |
| </span><span class="hll"><span class="linenos">180</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner</span><span class="p">,</span><span class="w"> </span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| </span><span class="linenos">181</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">scanner</span><span class="o">-></span><span class="n">ToTable</span><span class="p">();</span> |
| <span class="linenos">182</span><span class="p">}</span> |
| </pre></div> |
| </div> |
| <div class="admonition note"> |
| <p class="admonition-title">Note</p> |
| <p>Depending on the size of your dataset, this can require a lot of |
| memory; see <a class="reference internal" href="#cpp-dataset-filtering-data"><span class="std std-ref">Filtering data</span></a> below on |
| filtering/projecting.</p> |
| </div> |
| </section> |
| <section id="reading-different-file-formats"> |
| <h3>Reading different file formats<a class="headerlink" href="#reading-different-file-formats" title="Permalink to this heading">#</a></h3> |
| <p>The above examples use Parquet files on local disk, but the Dataset API |
| provides a consistent interface across multiple file formats and filesystems. |
| (See <a class="reference internal" href="#cpp-dataset-cloud-storage"><span class="std std-ref">Reading from cloud storage</span></a> for more information on the latter.) |
| Currently, Parquet, ORC, Feather / Arrow IPC, and CSV file formats are |
| supported; more formats are planned in the future.</p> |
| <p>If we save the table as Feather files instead of Parquet files:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos"> 90</span><span class="c1">// Set up a dataset by writing two Feather files.</span> |
| <span class="linenos"> 91</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span><span class="w"> </span><span class="n">CreateExampleFeatherDataset</span><span class="p">(</span> |
| <span class="linenos"> 92</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">root_path</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos"> 93</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">base_path</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">root_path</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">"/feather_dataset"</span><span class="p">;</span> |
| <span class="linenos"> 94</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">filesystem</span><span class="o">-></span><span class="n">CreateDir</span><span class="p">(</span><span class="n">base_path</span><span class="p">));</span> |
| <span class="linenos"> 95</span><span class="w"> </span><span class="c1">// Create an Arrow Table</span> |
| <span class="linenos"> 96</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">table</span><span class="p">,</span><span class="w"> </span><span class="n">CreateTable</span><span class="p">());</span> |
| <span class="linenos"> 97</span><span class="w"> </span><span class="c1">// Write it into two Feather files</span> |
| <span class="linenos"> 98</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">output</span><span class="p">,</span> |
| <span class="linenos"> 99</span><span class="w"> </span><span class="n">filesystem</span><span class="o">-></span><span class="n">OpenOutputStream</span><span class="p">(</span><span class="n">base_path</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">"/data1.feather"</span><span class="p">));</span> |
| <span class="linenos">100</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">writer</span><span class="p">,</span> |
| <span class="linenos">101</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">ipc</span><span class="o">::</span><span class="n">MakeFileWriter</span><span class="p">(</span><span class="n">output</span><span class="p">.</span><span class="n">get</span><span class="p">(),</span><span class="w"> </span><span class="n">table</span><span class="o">-></span><span class="n">schema</span><span class="p">()));</span> |
| <span class="linenos">102</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">writer</span><span class="o">-></span><span class="n">WriteTable</span><span class="p">(</span><span class="o">*</span><span class="n">table</span><span class="o">-></span><span class="n">Slice</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">)));</span> |
| <span class="linenos">103</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">writer</span><span class="o">-></span><span class="n">Close</span><span class="p">());</span> |
| <span class="linenos">104</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">output</span><span class="p">,</span> |
| <span class="linenos">105</span><span class="w"> </span><span class="n">filesystem</span><span class="o">-></span><span class="n">OpenOutputStream</span><span class="p">(</span><span class="n">base_path</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">"/data2.feather"</span><span class="p">));</span> |
| <span class="linenos">106</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">writer</span><span class="p">,</span> |
| <span class="linenos">107</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">ipc</span><span class="o">::</span><span class="n">MakeFileWriter</span><span class="p">(</span><span class="n">output</span><span class="p">.</span><span class="n">get</span><span class="p">(),</span><span class="w"> </span><span class="n">table</span><span class="o">-></span><span class="n">schema</span><span class="p">()));</span> |
| <span class="linenos">108</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">writer</span><span class="o">-></span><span class="n">WriteTable</span><span class="p">(</span><span class="o">*</span><span class="n">table</span><span class="o">-></span><span class="n">Slice</span><span class="p">(</span><span class="mi">5</span><span class="p">)));</span> |
| <span class="linenos">109</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">writer</span><span class="o">-></span><span class="n">Close</span><span class="p">());</span> |
| <span class="linenos">110</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">base_path</span><span class="p">;</span> |
| <span class="linenos">111</span><span class="p">}</span> |
| </pre></div> |
| </div> |
| <p>…then we can read the Feather file by passing an <a class="reference internal" href="api/dataset.html#_CPPv4N5arrow7dataset13IpcFileFormatE" title="arrow::dataset::IpcFileFormat"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::dataset::IpcFileFormat</span></code></a>:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="k">auto</span><span class="w"> </span><span class="n">format</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">ParquetFileFormat</span><span class="o">></span><span class="p">();</span> |
| <span class="c1">// ...</span> |
| <span class="k">auto</span><span class="w"> </span><span class="n">factory</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDatasetFactory</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="n">selector</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="n">options</span><span class="p">)</span> |
| <span class="w"> </span><span class="p">.</span><span class="n">ValueOrDie</span><span class="p">();</span> |
| </pre></div> |
| </div> |
| </section> |
| <section id="customizing-file-formats"> |
| <h3>Customizing file formats<a class="headerlink" href="#customizing-file-formats" title="Permalink to this heading">#</a></h3> |
| <p><a class="reference internal" href="api/dataset.html#_CPPv4N5arrow7dataset10FileFormatE" title="arrow::dataset::FileFormat"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::dataset::FileFormat</span></code></a> objects have properties that control how |
| files are read. For example:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="k">auto</span><span class="w"> </span><span class="n">format</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">ParquetFileFormat</span><span class="o">></span><span class="p">();</span> |
| <span class="n">format</span><span class="o">-></span><span class="n">reader_options</span><span class="p">.</span><span class="n">dict_columns</span><span class="p">.</span><span class="n">insert</span><span class="p">(</span><span class="s">"a"</span><span class="p">);</span> |
| </pre></div> |
| </div> |
| <p>Will configure column <code class="docutils literal notranslate"><span class="pre">"a"</span></code> to be dictionary-encoded when read. Similarly, |
| setting <a class="reference internal" href="api/dataset.html#_CPPv4N5arrow7dataset13CsvFileFormat13parse_optionsE" title="arrow::dataset::CsvFileFormat::parse_options"><code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">arrow::dataset::CsvFileFormat::parse_options</span></code></a> lets us change |
| things like reading comma-separated or tab-separated data.</p> |
| <p>Additionally, passing an <a class="reference internal" href="api/dataset.html#_CPPv4N5arrow7dataset19FragmentScanOptionsE" title="arrow::dataset::FragmentScanOptions"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::dataset::FragmentScanOptions</span></code></a> to |
| <a class="reference internal" href="api/dataset.html#_CPPv4N5arrow7dataset14ScannerBuilder19FragmentScanOptionsENSt10shared_ptrI19FragmentScanOptionsEE" title="arrow::dataset::ScannerBuilder::FragmentScanOptions"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">arrow::dataset::ScannerBuilder::FragmentScanOptions()</span></code></a> offers fine-grained |
| control over data scanning. For example, for CSV files, we can change what values |
| are converted into Boolean true and false at scan time.</p> |
| </section> |
| </section> |
| <section id="filtering-data"> |
| <span id="cpp-dataset-filtering-data"></span><h2>Filtering data<a class="headerlink" href="#filtering-data" title="Permalink to this heading">#</a></h2> |
| <p>So far, we’ve been reading the entire dataset, but if we need only a subset of the |
| data, this can waste time or memory reading data we don’t need. The |
| <a class="reference internal" href="api/dataset.html#_CPPv4N5arrow7dataset7ScannerE" title="arrow::dataset::Scanner"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::dataset::Scanner</span></code></a> offers control over what data to read.</p> |
| <p>In this snippet, we use <a class="reference internal" href="api/dataset.html#_CPPv4N5arrow7dataset14ScannerBuilder7ProjectENSt6vectorINSt6stringEEE" title="arrow::dataset::ScannerBuilder::Project"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">arrow::dataset::ScannerBuilder::Project()</span></code></a> to select |
| which columns to read:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos">186</span><span class="c1">// Read a dataset, but select only column "b" and only rows where b < 4.</span> |
| <span class="linenos">187</span><span class="c1">//</span> |
| <span class="linenos">188</span><span class="c1">// This is useful when you only want a few columns from a dataset. Where possible,</span> |
| <span class="linenos">189</span><span class="c1">// Datasets will push down the column selection such that less work is done.</span> |
| <span class="linenos">190</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">>></span><span class="w"> </span><span class="n">FilterAndSelectDataset</span><span class="p">(</span> |
| <span class="linenos">191</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span> |
| <span class="linenos">192</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">FileFormat</span><span class="o">>&</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">base_dir</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">193</span><span class="w"> </span><span class="n">fs</span><span class="o">::</span><span class="n">FileSelector</span><span class="w"> </span><span class="n">selector</span><span class="p">;</span> |
| <span class="linenos">194</span><span class="w"> </span><span class="n">selector</span><span class="p">.</span><span class="n">base_dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">base_dir</span><span class="p">;</span> |
| <span class="linenos">195</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span> |
| <span class="linenos">196</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">factory</span><span class="p">,</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDatasetFactory</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="n">selector</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span> |
| <span class="linenos">197</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemFactoryOptions</span><span class="p">()));</span> |
| <span class="linenos">198</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">dataset</span><span class="p">,</span><span class="w"> </span><span class="n">factory</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">199</span><span class="w"> </span><span class="c1">// Read specified columns with a row filter</span> |
| <span class="linenos">200</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scan_builder</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">NewScan</span><span class="p">());</span> |
| <span class="hll"><span class="linenos">201</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Project</span><span class="p">({</span><span class="s">"b"</span><span class="p">}));</span> |
| </span><span class="linenos">202</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Filter</span><span class="p">(</span><span class="n">cp</span><span class="o">::</span><span class="n">less</span><span class="p">(</span><span class="n">cp</span><span class="o">::</span><span class="n">field_ref</span><span class="p">(</span><span class="s">"b"</span><span class="p">),</span><span class="w"> </span><span class="n">cp</span><span class="o">::</span><span class="n">literal</span><span class="p">(</span><span class="mi">4</span><span class="p">))));</span> |
| <span class="linenos">203</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner</span><span class="p">,</span><span class="w"> </span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">204</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">scanner</span><span class="o">-></span><span class="n">ToTable</span><span class="p">();</span> |
| <span class="linenos">205</span><span class="p">}</span> |
| </pre></div> |
| </div> |
| <p>Some formats, such as Parquet, can reduce I/O costs here by reading only the |
| specified columns from the filesystem.</p> |
| <p>A filter can be provided with <a class="reference internal" href="api/dataset.html#_CPPv4N5arrow7dataset14ScannerBuilder6FilterERKN7compute10ExpressionE" title="arrow::dataset::ScannerBuilder::Filter"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">arrow::dataset::ScannerBuilder::Filter()</span></code></a>, so |
| that rows which do not match the filter predicate will not be included in the |
| returned table. Again, some formats, such as Parquet, can use this filter to |
| reduce the amount of I/O needed.</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos">186</span><span class="c1">// Read a dataset, but select only column "b" and only rows where b < 4.</span> |
| <span class="linenos">187</span><span class="c1">//</span> |
| <span class="linenos">188</span><span class="c1">// This is useful when you only want a few columns from a dataset. Where possible,</span> |
| <span class="linenos">189</span><span class="c1">// Datasets will push down the column selection such that less work is done.</span> |
| <span class="linenos">190</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">>></span><span class="w"> </span><span class="n">FilterAndSelectDataset</span><span class="p">(</span> |
| <span class="linenos">191</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span> |
| <span class="linenos">192</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">FileFormat</span><span class="o">>&</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">base_dir</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">193</span><span class="w"> </span><span class="n">fs</span><span class="o">::</span><span class="n">FileSelector</span><span class="w"> </span><span class="n">selector</span><span class="p">;</span> |
| <span class="linenos">194</span><span class="w"> </span><span class="n">selector</span><span class="p">.</span><span class="n">base_dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">base_dir</span><span class="p">;</span> |
| <span class="linenos">195</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span> |
| <span class="linenos">196</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">factory</span><span class="p">,</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDatasetFactory</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="n">selector</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span> |
| <span class="linenos">197</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemFactoryOptions</span><span class="p">()));</span> |
| <span class="linenos">198</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">dataset</span><span class="p">,</span><span class="w"> </span><span class="n">factory</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">199</span><span class="w"> </span><span class="c1">// Read specified columns with a row filter</span> |
| <span class="linenos">200</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scan_builder</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">NewScan</span><span class="p">());</span> |
| <span class="linenos">201</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Project</span><span class="p">({</span><span class="s">"b"</span><span class="p">}));</span> |
| <span class="hll"><span class="linenos">202</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Filter</span><span class="p">(</span><span class="n">cp</span><span class="o">::</span><span class="n">less</span><span class="p">(</span><span class="n">cp</span><span class="o">::</span><span class="n">field_ref</span><span class="p">(</span><span class="s">"b"</span><span class="p">),</span><span class="w"> </span><span class="n">cp</span><span class="o">::</span><span class="n">literal</span><span class="p">(</span><span class="mi">4</span><span class="p">))));</span> |
| </span><span class="linenos">203</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner</span><span class="p">,</span><span class="w"> </span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">204</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">scanner</span><span class="o">-></span><span class="n">ToTable</span><span class="p">();</span> |
| <span class="linenos">205</span><span class="p">}</span> |
| </pre></div> |
| </div> |
| </section> |
| <section id="projecting-columns"> |
| <h2>Projecting columns<a class="headerlink" href="#projecting-columns" title="Permalink to this heading">#</a></h2> |
| <p>In addition to selecting columns, <a class="reference internal" href="api/dataset.html#_CPPv4N5arrow7dataset14ScannerBuilder7ProjectENSt6vectorINSt6stringEEE" title="arrow::dataset::ScannerBuilder::Project"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">arrow::dataset::ScannerBuilder::Project()</span></code></a> |
| can also be used for more complex projections, such as renaming columns, casting |
| them to other types, and even deriving new columns based on evaluating |
| expressions.</p> |
| <p>In this case, we pass a vector of expressions used to construct column values |
| and a vector of names for the columns:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos">209</span><span class="c1">// Read a dataset, but with column projection.</span> |
| <span class="linenos">210</span><span class="c1">//</span> |
| <span class="linenos">211</span><span class="c1">// This is useful to derive new columns from existing data. For example, here we</span> |
| <span class="linenos">212</span><span class="c1">// demonstrate casting a column to a different type, and turning a numeric column into a</span> |
| <span class="linenos">213</span><span class="c1">// boolean column based on a predicate. You could also rename columns or perform</span> |
| <span class="linenos">214</span><span class="c1">// computations involving multiple columns.</span> |
| <span class="linenos">215</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">>></span><span class="w"> </span><span class="n">ProjectDataset</span><span class="p">(</span> |
| <span class="linenos">216</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span> |
| <span class="linenos">217</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">FileFormat</span><span class="o">>&</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">base_dir</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">218</span><span class="w"> </span><span class="n">fs</span><span class="o">::</span><span class="n">FileSelector</span><span class="w"> </span><span class="n">selector</span><span class="p">;</span> |
| <span class="linenos">219</span><span class="w"> </span><span class="n">selector</span><span class="p">.</span><span class="n">base_dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">base_dir</span><span class="p">;</span> |
| <span class="linenos">220</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span> |
| <span class="linenos">221</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">factory</span><span class="p">,</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDatasetFactory</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="n">selector</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span> |
| <span class="linenos">222</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemFactoryOptions</span><span class="p">()));</span> |
| <span class="linenos">223</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">dataset</span><span class="p">,</span><span class="w"> </span><span class="n">factory</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">224</span><span class="w"> </span><span class="c1">// Read specified columns with a row filter</span> |
| <span class="linenos">225</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scan_builder</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">NewScan</span><span class="p">());</span> |
| <span class="hll"><span class="linenos">226</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Project</span><span class="p">(</span> |
| </span><span class="hll"><span class="linenos">227</span><span class="w"> </span><span class="p">{</span> |
| </span><span class="hll"><span class="linenos">228</span><span class="w"> </span><span class="c1">// Leave column "a" as-is.</span> |
| </span><span class="hll"><span class="linenos">229</span><span class="w"> </span><span class="n">cp</span><span class="o">::</span><span class="n">field_ref</span><span class="p">(</span><span class="s">"a"</span><span class="p">),</span> |
| </span><span class="hll"><span class="linenos">230</span><span class="w"> </span><span class="c1">// Cast column "b" to float32.</span> |
| </span><span class="hll"><span class="linenos">231</span><span class="w"> </span><span class="n">cp</span><span class="o">::</span><span class="n">call</span><span class="p">(</span><span class="s">"cast"</span><span class="p">,</span><span class="w"> </span><span class="p">{</span><span class="n">cp</span><span class="o">::</span><span class="n">field_ref</span><span class="p">(</span><span class="s">"b"</span><span class="p">)},</span> |
| </span><span class="hll"><span class="linenos">232</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">compute</span><span class="o">::</span><span class="n">CastOptions</span><span class="o">::</span><span class="n">Safe</span><span class="p">(</span><span class="n">arrow</span><span class="o">::</span><span class="n">float32</span><span class="p">())),</span> |
| </span><span class="hll"><span class="linenos">233</span><span class="w"> </span><span class="c1">// Derive a boolean column from "c".</span> |
| </span><span class="hll"><span class="linenos">234</span><span class="w"> </span><span class="n">cp</span><span class="o">::</span><span class="n">equal</span><span class="p">(</span><span class="n">cp</span><span class="o">::</span><span class="n">field_ref</span><span class="p">(</span><span class="s">"c"</span><span class="p">),</span><span class="w"> </span><span class="n">cp</span><span class="o">::</span><span class="n">literal</span><span class="p">(</span><span class="mi">1</span><span class="p">)),</span> |
| </span><span class="hll"><span class="linenos">235</span><span class="w"> </span><span class="p">},</span> |
| </span><span class="hll"><span class="linenos">236</span><span class="w"> </span><span class="p">{</span><span class="s">"a_renamed"</span><span class="p">,</span><span class="w"> </span><span class="s">"b_as_float32"</span><span class="p">,</span><span class="w"> </span><span class="s">"c_1"</span><span class="p">}));</span> |
| </span><span class="linenos">237</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner</span><span class="p">,</span><span class="w"> </span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">238</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">scanner</span><span class="o">-></span><span class="n">ToTable</span><span class="p">();</span> |
| <span class="linenos">239</span><span class="p">}</span> |
| </pre></div> |
| </div> |
| <p>This also determines the column selection; only the given columns will be |
| present in the resulting table. If you want to include a derived column in |
| <em>addition</em> to the existing columns, you can build up the expressions from the |
| dataset schema:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos">243</span><span class="c1">// Read a dataset, but with column projection.</span> |
| <span class="linenos">244</span><span class="c1">//</span> |
| <span class="linenos">245</span><span class="c1">// This time, we read all original columns plus one derived column. This simply combines</span> |
| <span class="linenos">246</span><span class="c1">// the previous two examples: selecting a subset of columns by name, and deriving new</span> |
| <span class="linenos">247</span><span class="c1">// columns with an expression.</span> |
| <span class="linenos">248</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">>></span><span class="w"> </span><span class="n">SelectAndProjectDataset</span><span class="p">(</span> |
| <span class="linenos">249</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span> |
| <span class="linenos">250</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">FileFormat</span><span class="o">>&</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">base_dir</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">251</span><span class="w"> </span><span class="n">fs</span><span class="o">::</span><span class="n">FileSelector</span><span class="w"> </span><span class="n">selector</span><span class="p">;</span> |
| <span class="linenos">252</span><span class="w"> </span><span class="n">selector</span><span class="p">.</span><span class="n">base_dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">base_dir</span><span class="p">;</span> |
| <span class="linenos">253</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span> |
| <span class="linenos">254</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">factory</span><span class="p">,</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDatasetFactory</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="n">selector</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span> |
| <span class="linenos">255</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemFactoryOptions</span><span class="p">()));</span> |
| <span class="linenos">256</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">dataset</span><span class="p">,</span><span class="w"> </span><span class="n">factory</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">257</span><span class="w"> </span><span class="c1">// Read specified columns with a row filter</span> |
| <span class="linenos">258</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scan_builder</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">NewScan</span><span class="p">());</span> |
| <span class="hll"><span class="linenos">259</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span><span class="w"> </span><span class="n">names</span><span class="p">;</span> |
| </span><span class="hll"><span class="linenos">260</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">cp</span><span class="o">::</span><span class="n">Expression</span><span class="o">></span><span class="w"> </span><span class="n">exprs</span><span class="p">;</span> |
| </span><span class="hll"><span class="linenos">261</span><span class="w"> </span><span class="c1">// Read all the original columns.</span> |
| </span><span class="hll"><span class="linenos">262</span><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="k">auto</span><span class="o">&</span><span class="w"> </span><span class="n">field</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">schema</span><span class="p">()</span><span class="o">-></span><span class="n">fields</span><span class="p">())</span><span class="w"> </span><span class="p">{</span> |
| </span><span class="hll"><span class="linenos">263</span><span class="w"> </span><span class="n">names</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">field</span><span class="o">-></span><span class="n">name</span><span class="p">());</span> |
| </span><span class="hll"><span class="linenos">264</span><span class="w"> </span><span class="n">exprs</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">cp</span><span class="o">::</span><span class="n">field_ref</span><span class="p">(</span><span class="n">field</span><span class="o">-></span><span class="n">name</span><span class="p">()));</span> |
| </span><span class="hll"><span class="linenos">265</span><span class="w"> </span><span class="p">}</span> |
| </span><span class="hll"><span class="linenos">266</span><span class="w"> </span><span class="c1">// Also derive a new column.</span> |
| </span><span class="hll"><span class="linenos">267</span><span class="w"> </span><span class="n">names</span><span class="p">.</span><span class="n">emplace_back</span><span class="p">(</span><span class="s">"b_large"</span><span class="p">);</span> |
| </span><span class="hll"><span class="linenos">268</span><span class="w"> </span><span class="n">exprs</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">cp</span><span class="o">::</span><span class="n">greater</span><span class="p">(</span><span class="n">cp</span><span class="o">::</span><span class="n">field_ref</span><span class="p">(</span><span class="s">"b"</span><span class="p">),</span><span class="w"> </span><span class="n">cp</span><span class="o">::</span><span class="n">literal</span><span class="p">(</span><span class="mi">1</span><span class="p">)));</span> |
| </span><span class="hll"><span class="linenos">269</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Project</span><span class="p">(</span><span class="n">exprs</span><span class="p">,</span><span class="w"> </span><span class="n">names</span><span class="p">));</span> |
| </span><span class="linenos">270</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner</span><span class="p">,</span><span class="w"> </span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">271</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">scanner</span><span class="o">-></span><span class="n">ToTable</span><span class="p">();</span> |
| <span class="linenos">272</span><span class="p">}</span> |
| </pre></div> |
| </div> |
| <div class="admonition note"> |
| <p class="admonition-title">Note</p> |
| <p>When combining filters and projections, Arrow will determine all |
| necessary columns to read. For instance, if you filter on a column that |
| isn’t ultimately selected, Arrow will still read the column to evaluate |
| the filter.</p> |
| </div> |
| </section> |
| <section id="reading-and-writing-partitioned-data"> |
| <h2>Reading and writing partitioned data<a class="headerlink" href="#reading-and-writing-partitioned-data" title="Permalink to this heading">#</a></h2> |
| <p>So far, we’ve been working with datasets consisting of flat directories with |
| files. Oftentimes, a dataset will have one or more columns that are frequently |
| filtered on. Instead of having to read and then filter the data, by organizing the |
| files into a nested directory structure, we can define a partitioned dataset, |
| where sub-directory names hold information about which subset of the data is |
| stored in that directory. Then, we can more efficiently filter data by using that |
| information to avoid loading files that don’t match the filter.</p> |
| <p>For example, a dataset partitioned by year and month may have the following layout:</p> |
| <div class="highlight-text notranslate"><div class="highlight"><pre><span></span>dataset_name/ |
| year=2007/ |
| month=01/ |
| data0.parquet |
| data1.parquet |
| ... |
| month=02/ |
| data0.parquet |
| data1.parquet |
| ... |
| month=03/ |
| ... |
| year=2008/ |
| month=01/ |
| ... |
| ... |
| </pre></div> |
| </div> |
| <p>The above partitioning scheme is using “/key=value/” directory names, as found in |
| Apache Hive. Under this convention, the file at |
| <code class="docutils literal notranslate"><span class="pre">dataset_name/year=2007/month=01/data0.parquet</span></code> contains only data for which |
| <code class="docutils literal notranslate"><span class="pre">year</span> <span class="pre">==</span> <span class="pre">2007</span></code> and <code class="docutils literal notranslate"><span class="pre">month</span> <span class="pre">==</span> <span class="pre">01</span></code>.</p> |
| <p>Let’s create a small partitioned dataset. For this, we’ll use Arrow’s dataset |
| writing functionality.</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos">115</span><span class="c1">// Set up a dataset by writing files with partitioning</span> |
| <span class="linenos">116</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span><span class="w"> </span><span class="n">CreateExampleParquetHivePartitionedDataset</span><span class="p">(</span> |
| <span class="linenos">117</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">root_path</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">118</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">base_path</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">root_path</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">"/parquet_dataset"</span><span class="p">;</span> |
| <span class="linenos">119</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">filesystem</span><span class="o">-></span><span class="n">CreateDir</span><span class="p">(</span><span class="n">base_path</span><span class="p">));</span> |
| <span class="linenos">120</span><span class="w"> </span><span class="c1">// Create an Arrow Table</span> |
| <span class="linenos">121</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">schema</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">schema</span><span class="p">(</span> |
| <span class="linenos">122</span><span class="w"> </span><span class="p">{</span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">int64</span><span class="p">()),</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"b"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">int64</span><span class="p">()),</span> |
| <span class="linenos">123</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"c"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">int64</span><span class="p">()),</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"part"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">utf8</span><span class="p">())});</span> |
| <span class="linenos">124</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Array</span><span class="o">>></span><span class="w"> </span><span class="n">arrays</span><span class="p">(</span><span class="mi">4</span><span class="p">);</span> |
| <span class="linenos">125</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">NumericBuilder</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Int64Type</span><span class="o">></span><span class="w"> </span><span class="n">builder</span><span class="p">;</span> |
| <span class="linenos">126</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">({</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">9</span><span class="p">}));</span> |
| <span class="linenos">127</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">(</span><span class="o">&</span><span class="n">arrays</span><span class="p">[</span><span class="mi">0</span><span class="p">]));</span> |
| <span class="linenos">128</span><span class="w"> </span><span class="n">builder</span><span class="p">.</span><span class="n">Reset</span><span class="p">();</span> |
| <span class="linenos">129</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">({</span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">}));</span> |
| <span class="linenos">130</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">(</span><span class="o">&</span><span class="n">arrays</span><span class="p">[</span><span class="mi">1</span><span class="p">]));</span> |
| <span class="linenos">131</span><span class="w"> </span><span class="n">builder</span><span class="p">.</span><span class="n">Reset</span><span class="p">();</span> |
| <span class="linenos">132</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">({</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">}));</span> |
| <span class="linenos">133</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">(</span><span class="o">&</span><span class="n">arrays</span><span class="p">[</span><span class="mi">2</span><span class="p">]));</span> |
| <span class="linenos">134</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">StringBuilder</span><span class="w"> </span><span class="n">string_builder</span><span class="p">;</span> |
| <span class="linenos">135</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span> |
| <span class="linenos">136</span><span class="w"> </span><span class="n">string_builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">({</span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="s">"b"</span><span class="p">,</span><span class="w"> </span><span class="s">"b"</span><span class="p">,</span><span class="w"> </span><span class="s">"b"</span><span class="p">,</span><span class="w"> </span><span class="s">"b"</span><span class="p">,</span><span class="w"> </span><span class="s">"b"</span><span class="p">}));</span> |
| <span class="linenos">137</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">string_builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">(</span><span class="o">&</span><span class="n">arrays</span><span class="p">[</span><span class="mi">3</span><span class="p">]));</span> |
| <span class="linenos">138</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">table</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span><span class="n">schema</span><span class="p">,</span><span class="w"> </span><span class="n">arrays</span><span class="p">);</span> |
| <span class="hll"><span class="linenos">139</span><span class="w"> </span><span class="c1">// Write it using Datasets</span> |
| </span><span class="hll"><span class="linenos">140</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">dataset</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">InMemoryDataset</span><span class="o">></span><span class="p">(</span><span class="n">table</span><span class="p">);</span> |
| </span><span class="hll"><span class="linenos">141</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner_builder</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">NewScan</span><span class="p">());</span> |
| </span><span class="hll"><span class="linenos">142</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner</span><span class="p">,</span><span class="w"> </span><span class="n">scanner_builder</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| </span><span class="hll"><span class="linenos">143</span> |
| </span><span class="hll"><span class="linenos">144</span><span class="w"> </span><span class="c1">// The partition schema determines which fields are part of the partitioning.</span> |
| </span><span class="hll"><span class="linenos">145</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">partition_schema</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">schema</span><span class="p">({</span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"part"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">utf8</span><span class="p">())});</span> |
| </span><span class="hll"><span class="linenos">146</span><span class="w"> </span><span class="c1">// We'll use Hive-style partitioning, which creates directories with "key=value" pairs.</span> |
| </span><span class="hll"><span class="linenos">147</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">partitioning</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">HivePartitioning</span><span class="o">></span><span class="p">(</span><span class="n">partition_schema</span><span class="p">);</span> |
| </span><span class="hll"><span class="linenos">148</span><span class="w"> </span><span class="c1">// We'll write Parquet files.</span> |
| </span><span class="hll"><span class="linenos">149</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">format</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">ParquetFileFormat</span><span class="o">></span><span class="p">();</span> |
| </span><span class="hll"><span class="linenos">150</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDatasetWriteOptions</span><span class="w"> </span><span class="n">write_options</span><span class="p">;</span> |
| </span><span class="hll"><span class="linenos">151</span><span class="w"> </span><span class="n">write_options</span><span class="p">.</span><span class="n">file_write_options</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">format</span><span class="o">-></span><span class="n">DefaultWriteOptions</span><span class="p">();</span> |
| </span><span class="hll"><span class="linenos">152</span><span class="w"> </span><span class="n">write_options</span><span class="p">.</span><span class="n">filesystem</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">filesystem</span><span class="p">;</span> |
| </span><span class="hll"><span class="linenos">153</span><span class="w"> </span><span class="n">write_options</span><span class="p">.</span><span class="n">base_dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">base_path</span><span class="p">;</span> |
| </span><span class="hll"><span class="linenos">154</span><span class="w"> </span><span class="n">write_options</span><span class="p">.</span><span class="n">partitioning</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">partitioning</span><span class="p">;</span> |
| </span><span class="hll"><span class="linenos">155</span><span class="w"> </span><span class="n">write_options</span><span class="p">.</span><span class="n">basename_template</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"part{i}.parquet"</span><span class="p">;</span> |
| </span><span class="hll"><span class="linenos">156</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDataset</span><span class="o">::</span><span class="n">Write</span><span class="p">(</span><span class="n">write_options</span><span class="p">,</span><span class="w"> </span><span class="n">scanner</span><span class="p">));</span> |
| </span><span class="linenos">157</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">base_path</span><span class="p">;</span> |
| <span class="linenos">158</span><span class="p">}</span> |
| </pre></div> |
| </div> |
| <p>The above created a directory with two subdirectories (“part=a” and “part=b”), |
| and the Parquet files written in those directories no longer include the “part” |
| column.</p> |
| <p>Reading this dataset, we now specify that the dataset should use a Hive-like |
| partitioning scheme:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos">276</span><span class="c1">// Read an entire dataset, but with partitioning information.</span> |
| <span class="linenos">277</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">>></span><span class="w"> </span><span class="n">ScanPartitionedDataset</span><span class="p">(</span> |
| <span class="linenos">278</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span> |
| <span class="linenos">279</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">FileFormat</span><span class="o">>&</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">base_dir</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">280</span><span class="w"> </span><span class="n">fs</span><span class="o">::</span><span class="n">FileSelector</span><span class="w"> </span><span class="n">selector</span><span class="p">;</span> |
| <span class="linenos">281</span><span class="w"> </span><span class="n">selector</span><span class="p">.</span><span class="n">base_dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">base_dir</span><span class="p">;</span> |
| <span class="hll"><span class="linenos">282</span><span class="w"> </span><span class="n">selector</span><span class="p">.</span><span class="n">recursive</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">true</span><span class="p">;</span><span class="w"> </span><span class="c1">// Make sure to search subdirectories</span> |
| </span><span class="linenos">283</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemFactoryOptions</span><span class="w"> </span><span class="n">options</span><span class="p">;</span> |
| <span class="hll"><span class="linenos">284</span><span class="w"> </span><span class="c1">// We'll use Hive-style partitioning. We'll let Arrow Datasets infer the partition</span> |
| </span><span class="hll"><span class="linenos">285</span><span class="w"> </span><span class="c1">// schema.</span> |
| </span><span class="hll"><span class="linenos">286</span><span class="w"> </span><span class="n">options</span><span class="p">.</span><span class="n">partitioning</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">HivePartitioning</span><span class="o">::</span><span class="n">MakeFactory</span><span class="p">();</span> |
| </span><span class="linenos">287</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">factory</span><span class="p">,</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDatasetFactory</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span> |
| <span class="linenos">288</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="n">selector</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="n">options</span><span class="p">));</span> |
| <span class="linenos">289</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">dataset</span><span class="p">,</span><span class="w"> </span><span class="n">factory</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">290</span><span class="w"> </span><span class="c1">// Print out the fragments</span> |
| <span class="linenos">291</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">fragments</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">GetFragments</span><span class="p">());</span> |
| <span class="linenos">292</span><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="k">auto</span><span class="o">&</span><span class="w"> </span><span class="n">fragment</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">fragments</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">293</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"Found fragment: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">fragment</span><span class="p">)</span><span class="o">-></span><span class="n">ToString</span><span class="p">()</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> |
| <span class="linenos">294</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"Partition expression: "</span> |
| <span class="linenos">295</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">fragment</span><span class="p">)</span><span class="o">-></span><span class="n">partition_expression</span><span class="p">().</span><span class="n">ToString</span><span class="p">()</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> |
| <span class="linenos">296</span><span class="w"> </span><span class="p">}</span> |
| <span class="linenos">297</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scan_builder</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">NewScan</span><span class="p">());</span> |
| <span class="linenos">298</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner</span><span class="p">,</span><span class="w"> </span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">299</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">scanner</span><span class="o">-></span><span class="n">ToTable</span><span class="p">();</span> |
| <span class="linenos">300</span><span class="p">}</span> |
| </pre></div> |
| </div> |
| <p>Although the partition fields are not included in the actual Parquet files, |
| they will be added back to the resulting table when scanning this dataset:</p> |
| <div class="highlight-text notranslate"><div class="highlight"><pre><span></span>$ ./debug/dataset_documentation_example file:///tmp parquet_hive partitioned |
| Found fragment: /tmp/parquet_dataset/part=a/part0.parquet |
| Partition expression: (part == "a") |
| Found fragment: /tmp/parquet_dataset/part=b/part1.parquet |
| Partition expression: (part == "b") |
| Read 20 rows |
| a: int64 |
| -- field metadata -- |
| PARQUET:field_id: '1' |
| b: double |
| -- field metadata -- |
| PARQUET:field_id: '2' |
| c: int64 |
| -- field metadata -- |
| PARQUET:field_id: '3' |
| part: string |
| ---- |
| # snip... |
| </pre></div> |
| </div> |
| <p>We can now filter on the partition keys, which avoids loading files |
| altogether if they do not match the filter:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos">304</span><span class="c1">// Read an entire dataset, but with partitioning information. Also, filter the dataset on</span> |
| <span class="linenos">305</span><span class="c1">// the partition values.</span> |
| <span class="linenos">306</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">>></span><span class="w"> </span><span class="n">FilterPartitionedDataset</span><span class="p">(</span> |
| <span class="linenos">307</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span> |
| <span class="linenos">308</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">FileFormat</span><span class="o">>&</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">base_dir</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">309</span><span class="w"> </span><span class="n">fs</span><span class="o">::</span><span class="n">FileSelector</span><span class="w"> </span><span class="n">selector</span><span class="p">;</span> |
| <span class="linenos">310</span><span class="w"> </span><span class="n">selector</span><span class="p">.</span><span class="n">base_dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">base_dir</span><span class="p">;</span> |
| <span class="linenos">311</span><span class="w"> </span><span class="n">selector</span><span class="p">.</span><span class="n">recursive</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">true</span><span class="p">;</span> |
| <span class="linenos">312</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemFactoryOptions</span><span class="w"> </span><span class="n">options</span><span class="p">;</span> |
| <span class="linenos">313</span><span class="w"> </span><span class="n">options</span><span class="p">.</span><span class="n">partitioning</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">HivePartitioning</span><span class="o">::</span><span class="n">MakeFactory</span><span class="p">();</span> |
| <span class="linenos">314</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">factory</span><span class="p">,</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDatasetFactory</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span> |
| <span class="linenos">315</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="n">selector</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="n">options</span><span class="p">));</span> |
| <span class="linenos">316</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">dataset</span><span class="p">,</span><span class="w"> </span><span class="n">factory</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">317</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scan_builder</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">NewScan</span><span class="p">());</span> |
| <span class="hll"><span class="linenos">318</span><span class="w"> </span><span class="c1">// Filter based on the partition values. This will mean that we won't even read the</span> |
| </span><span class="hll"><span class="linenos">319</span><span class="w"> </span><span class="c1">// files whose partition expressions don't match the filter.</span> |
| </span><span class="hll"><span class="linenos">320</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span> |
| </span><span class="hll"><span class="linenos">321</span><span class="w"> </span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Filter</span><span class="p">(</span><span class="n">cp</span><span class="o">::</span><span class="n">equal</span><span class="p">(</span><span class="n">cp</span><span class="o">::</span><span class="n">field_ref</span><span class="p">(</span><span class="s">"part"</span><span class="p">),</span><span class="w"> </span><span class="n">cp</span><span class="o">::</span><span class="n">literal</span><span class="p">(</span><span class="s">"b"</span><span class="p">))));</span> |
| </span><span class="linenos">322</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner</span><span class="p">,</span><span class="w"> </span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">323</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">scanner</span><span class="o">-></span><span class="n">ToTable</span><span class="p">();</span> |
| <span class="linenos">324</span><span class="p">}</span> |
| </pre></div> |
| </div> |
| <section id="different-partitioning-schemes"> |
| <h3>Different partitioning schemes<a class="headerlink" href="#different-partitioning-schemes" title="Permalink to this heading">#</a></h3> |
| <p>The above example uses a Hive-like directory scheme, such as “/year=2009/month=11/day=15”. |
| We specified this by passing the Hive partitioning factory. In this case, the types of |
| the partition keys are inferred from the file paths.</p> |
| <p>It is also possible to directly construct the partitioning and explicitly define |
| the schema of the partition keys. For example:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="k">auto</span><span class="w"> </span><span class="n">part</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">HivePartitioning</span><span class="o">></span><span class="p">(</span><span class="n">arrow</span><span class="o">::</span><span class="n">schema</span><span class="p">({</span> |
| <span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"year"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">int16</span><span class="p">()),</span> |
| <span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"month"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">int8</span><span class="p">()),</span> |
| <span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"day"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">int32</span><span class="p">())</span> |
| <span class="p">}));</span> |
| </pre></div> |
| </div> |
| <p>Arrow supports another partitioning scheme, “directory partitioning”, where the |
| segments in the file path represent the values of the partition keys without |
| including the name (the field names are implicit in the segment’s index). For |
| example, given field names “year”, “month”, and “day”, one path might be |
| “/2019/11/15”.</p> |
| <p>Since the names are not included in the file paths, these must be specified |
| when constructing a directory partitioning:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="k">auto</span><span class="w"> </span><span class="n">part</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">DirectoryPartitioning</span><span class="o">::</span><span class="n">MakeFactory</span><span class="p">({</span><span class="s">"year"</span><span class="p">,</span><span class="w"> </span><span class="s">"month"</span><span class="p">,</span><span class="w"> </span><span class="s">"day"</span><span class="p">});</span> |
| </pre></div> |
| </div> |
| <p>Directory partitioning also supports providing a full schema rather than inferring |
| types from file paths.</p> |
| </section> |
| <section id="partitioning-performance-considerations"> |
| <h3>Partitioning performance considerations<a class="headerlink" href="#partitioning-performance-considerations" title="Permalink to this heading">#</a></h3> |
| <p>Partitioning datasets has two aspects that affect performance: it increases the number of |
| files and it creates a directory structure around the files. Both of these have benefits |
| as well as costs. Depending on the configuration and the size of your dataset, the costs |
| can outweigh the benefits.</p> |
| <p>Because partitions split up the dataset into multiple files, partitioned datasets can be |
| read and written with parallelism. However, each additional file adds a little overhead in |
| processing for filesystem interaction. It also increases the overall dataset size since |
| each file has some shared metadata. For example, each parquet file contains the schema and |
| group-level statistics. The number of partitions is a floor for the number of files. If |
| you partition a dataset by date with a year of data, you will have at least 365 files. If |
| you further partition by another dimension with 1,000 unique values, you will have up to |
| 365,000 files. This fine of partitioning often leads to small files that mostly consist of |
| metadata.</p> |
| <p>Partitioned datasets create nested folder structures, and those allow us to prune which |
| files are loaded in a scan. However, this adds overhead to discovering files in the dataset, |
| as we’ll need to recursively “list directory” to find the data files. Too fine |
| partitions can cause problems here: Partitioning a dataset by date for a years worth |
| of data will require 365 list calls to find all the files; adding another column with |
| cardinality 1,000 will make that 365,365 calls.</p> |
| <p>The most optimal partitioning layout will depend on your data, access patterns, and which |
| systems will be reading the data. Most systems, including Arrow, should work across a |
| range of file sizes and partitioning layouts, but there are extremes you should avoid. These |
| guidelines can help avoid some known worst cases:</p> |
| <ul class="simple"> |
| <li><p>Avoid files smaller than 20MB and larger than 2GB.</p></li> |
| <li><p>Avoid partitioning layouts with more than 10,000 distinct partitions.</p></li> |
| </ul> |
| <p>For file formats that have a notion of groups within a file, such as Parquet, similar |
| guidelines apply. Row groups can provide parallelism when reading and allow data skipping |
| based on statistics, but very small groups can cause metadata to be a significant portion |
| of file size. Arrow’s file writer provides sensible defaults for group sizing in most cases.</p> |
| </section> |
| </section> |
| <section id="reading-from-other-data-sources"> |
| <h2>Reading from other data sources<a class="headerlink" href="#reading-from-other-data-sources" title="Permalink to this heading">#</a></h2> |
| <section id="reading-in-memory-data"> |
| <h3>Reading in-memory data<a class="headerlink" href="#reading-in-memory-data" title="Permalink to this heading">#</a></h3> |
| <p>If you already have data in memory that you’d like to use with the Datasets API |
| (e.g. to filter/project data, or to write it out to a filesystem), you can wrap it |
| in an <a class="reference internal" href="api/dataset.html#_CPPv4N5arrow7dataset15InMemoryDatasetE" title="arrow::dataset::InMemoryDataset"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::dataset::InMemoryDataset</span></code></a>:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="k">auto</span><span class="w"> </span><span class="n">table</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">::</span><span class="n">FromRecordBatches</span><span class="p">(...);</span> |
| <span class="k">auto</span><span class="w"> </span><span class="n">dataset</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">dataset</span><span class="o">::</span><span class="n">InMemoryDataset</span><span class="o">></span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">move</span><span class="p">(</span><span class="n">table</span><span class="p">));</span> |
| <span class="c1">// Scan the dataset, filter, it, etc.</span> |
| <span class="k">auto</span><span class="w"> </span><span class="n">scanner_builder</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">NewScan</span><span class="p">();</span> |
| </pre></div> |
| </div> |
| <p>In the example, we used the InMemoryDataset to write our example data to local |
| disk which was used in the rest of the example:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos">115</span><span class="c1">// Set up a dataset by writing files with partitioning</span> |
| <span class="linenos">116</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span><span class="w"> </span><span class="n">CreateExampleParquetHivePartitionedDataset</span><span class="p">(</span> |
| <span class="linenos">117</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">root_path</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">118</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">base_path</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">root_path</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">"/parquet_dataset"</span><span class="p">;</span> |
| <span class="linenos">119</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">filesystem</span><span class="o">-></span><span class="n">CreateDir</span><span class="p">(</span><span class="n">base_path</span><span class="p">));</span> |
| <span class="linenos">120</span><span class="w"> </span><span class="c1">// Create an Arrow Table</span> |
| <span class="linenos">121</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">schema</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">schema</span><span class="p">(</span> |
| <span class="linenos">122</span><span class="w"> </span><span class="p">{</span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">int64</span><span class="p">()),</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"b"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">int64</span><span class="p">()),</span> |
| <span class="linenos">123</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"c"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">int64</span><span class="p">()),</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"part"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">utf8</span><span class="p">())});</span> |
| <span class="linenos">124</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Array</span><span class="o">>></span><span class="w"> </span><span class="n">arrays</span><span class="p">(</span><span class="mi">4</span><span class="p">);</span> |
| <span class="linenos">125</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">NumericBuilder</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Int64Type</span><span class="o">></span><span class="w"> </span><span class="n">builder</span><span class="p">;</span> |
| <span class="linenos">126</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">({</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">9</span><span class="p">}));</span> |
| <span class="linenos">127</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">(</span><span class="o">&</span><span class="n">arrays</span><span class="p">[</span><span class="mi">0</span><span class="p">]));</span> |
| <span class="linenos">128</span><span class="w"> </span><span class="n">builder</span><span class="p">.</span><span class="n">Reset</span><span class="p">();</span> |
| <span class="linenos">129</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">({</span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">}));</span> |
| <span class="linenos">130</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">(</span><span class="o">&</span><span class="n">arrays</span><span class="p">[</span><span class="mi">1</span><span class="p">]));</span> |
| <span class="linenos">131</span><span class="w"> </span><span class="n">builder</span><span class="p">.</span><span class="n">Reset</span><span class="p">();</span> |
| <span class="linenos">132</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">({</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">}));</span> |
| <span class="linenos">133</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">(</span><span class="o">&</span><span class="n">arrays</span><span class="p">[</span><span class="mi">2</span><span class="p">]));</span> |
| <span class="linenos">134</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">StringBuilder</span><span class="w"> </span><span class="n">string_builder</span><span class="p">;</span> |
| <span class="linenos">135</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span> |
| <span class="linenos">136</span><span class="w"> </span><span class="n">string_builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">({</span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="s">"b"</span><span class="p">,</span><span class="w"> </span><span class="s">"b"</span><span class="p">,</span><span class="w"> </span><span class="s">"b"</span><span class="p">,</span><span class="w"> </span><span class="s">"b"</span><span class="p">,</span><span class="w"> </span><span class="s">"b"</span><span class="p">}));</span> |
| <span class="linenos">137</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">string_builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">(</span><span class="o">&</span><span class="n">arrays</span><span class="p">[</span><span class="mi">3</span><span class="p">]));</span> |
| <span class="hll"><span class="linenos">138</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">table</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span><span class="n">schema</span><span class="p">,</span><span class="w"> </span><span class="n">arrays</span><span class="p">);</span> |
| </span><span class="hll"><span class="linenos">139</span><span class="w"> </span><span class="c1">// Write it using Datasets</span> |
| </span><span class="hll"><span class="linenos">140</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">dataset</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">InMemoryDataset</span><span class="o">></span><span class="p">(</span><span class="n">table</span><span class="p">);</span> |
| </span><span class="hll"><span class="linenos">141</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner_builder</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">NewScan</span><span class="p">());</span> |
| </span><span class="hll"><span class="linenos">142</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner</span><span class="p">,</span><span class="w"> </span><span class="n">scanner_builder</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| </span><span class="linenos">143</span> |
| <span class="linenos">144</span><span class="w"> </span><span class="c1">// The partition schema determines which fields are part of the partitioning.</span> |
| <span class="linenos">145</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">partition_schema</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">schema</span><span class="p">({</span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"part"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">utf8</span><span class="p">())});</span> |
| <span class="linenos">146</span><span class="w"> </span><span class="c1">// We'll use Hive-style partitioning, which creates directories with "key=value" pairs.</span> |
| <span class="linenos">147</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">partitioning</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">HivePartitioning</span><span class="o">></span><span class="p">(</span><span class="n">partition_schema</span><span class="p">);</span> |
| <span class="linenos">148</span><span class="w"> </span><span class="c1">// We'll write Parquet files.</span> |
| <span class="linenos">149</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">format</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">ParquetFileFormat</span><span class="o">></span><span class="p">();</span> |
| <span class="linenos">150</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDatasetWriteOptions</span><span class="w"> </span><span class="n">write_options</span><span class="p">;</span> |
| <span class="linenos">151</span><span class="w"> </span><span class="n">write_options</span><span class="p">.</span><span class="n">file_write_options</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">format</span><span class="o">-></span><span class="n">DefaultWriteOptions</span><span class="p">();</span> |
| <span class="linenos">152</span><span class="w"> </span><span class="n">write_options</span><span class="p">.</span><span class="n">filesystem</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">filesystem</span><span class="p">;</span> |
| <span class="linenos">153</span><span class="w"> </span><span class="n">write_options</span><span class="p">.</span><span class="n">base_dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">base_path</span><span class="p">;</span> |
| <span class="linenos">154</span><span class="w"> </span><span class="n">write_options</span><span class="p">.</span><span class="n">partitioning</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">partitioning</span><span class="p">;</span> |
| <span class="linenos">155</span><span class="w"> </span><span class="n">write_options</span><span class="p">.</span><span class="n">basename_template</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"part{i}.parquet"</span><span class="p">;</span> |
| <span class="linenos">156</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDataset</span><span class="o">::</span><span class="n">Write</span><span class="p">(</span><span class="n">write_options</span><span class="p">,</span><span class="w"> </span><span class="n">scanner</span><span class="p">));</span> |
| <span class="linenos">157</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">base_path</span><span class="p">;</span> |
| <span class="linenos">158</span><span class="p">}</span> |
| </pre></div> |
| </div> |
| </section> |
| <section id="reading-from-cloud-storage"> |
| <span id="cpp-dataset-cloud-storage"></span><h3>Reading from cloud storage<a class="headerlink" href="#reading-from-cloud-storage" title="Permalink to this heading">#</a></h3> |
| <p>In addition to local files, Arrow Datasets also support reading from cloud |
| storage systems, such as Amazon S3, by passing a different filesystem.</p> |
| <p>See the <a class="reference internal" href="io.html#cpp-filesystems"><span class="std std-ref">filesystem</span></a> docs for more details on the available |
| filesystems.</p> |
| </section> |
| </section> |
| <section id="a-note-on-transactions-acid-guarantees"> |
| <span id="cpp-dataset-full-example"></span><h2>A note on transactions & ACID guarantees<a class="headerlink" href="#a-note-on-transactions-acid-guarantees" title="Permalink to this heading">#</a></h2> |
| <p>The dataset API offers no transaction support or any ACID guarantees. This affects |
| both reading and writing. Concurrent reads are fine. Concurrent writes or writes |
| concurring with reads may have unexpected behavior. Various approaches can be used |
| to avoid operating on the same files such as using a unique basename template for |
| each writer, a temporary directory for new files, or separate storage of the file |
| list instead of relying on directory discovery.</p> |
| <p>Unexpectedly killing the process while a write is in progress can leave the system |
| in an inconsistent state. Write calls generally return as soon as the bytes to be |
| written have been completely delivered to the OS page cache. Even though a write |
| operation has been completed it is possible for part of the file to be lost if |
| there is a sudden power loss immediately after the write call.</p> |
| <p>Most file formats have magic numbers which are written at the end. This means a |
| partial file write can safely be detected and discarded. The CSV file format does |
| not have any such concept and a partially written CSV file may be detected as valid.</p> |
| </section> |
| <section id="full-example"> |
| <h2>Full Example<a class="headerlink" href="#full-example" title="Permalink to this heading">#</a></h2> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos"> 1</span><span class="c1">// Licensed to the Apache Software Foundation (ASF) under one</span> |
| <span class="linenos"> 2</span><span class="c1">// or more contributor license agreements. See the NOTICE file</span> |
| <span class="linenos"> 3</span><span class="c1">// distributed with this work for additional information</span> |
| <span class="linenos"> 4</span><span class="c1">// regarding copyright ownership. The ASF licenses this file</span> |
| <span class="linenos"> 5</span><span class="c1">// to you under the Apache License, Version 2.0 (the</span> |
| <span class="linenos"> 6</span><span class="c1">// "License"); you may not use this file except in compliance</span> |
| <span class="linenos"> 7</span><span class="c1">// with the License. You may obtain a copy of the License at</span> |
| <span class="linenos"> 8</span><span class="c1">//</span> |
| <span class="linenos"> 9</span><span class="c1">// http://www.apache.org/licenses/LICENSE-2.0</span> |
| <span class="linenos"> 10</span><span class="c1">//</span> |
| <span class="linenos"> 11</span><span class="c1">// Unless required by applicable law or agreed to in writing,</span> |
| <span class="linenos"> 12</span><span class="c1">// software distributed under the License is distributed on an</span> |
| <span class="linenos"> 13</span><span class="c1">// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY</span> |
| <span class="linenos"> 14</span><span class="c1">// KIND, either express or implied. See the License for the</span> |
| <span class="linenos"> 15</span><span class="c1">// specific language governing permissions and limitations</span> |
| <span class="linenos"> 16</span><span class="c1">// under the License.</span> |
| <span class="linenos"> 17</span> |
| <span class="linenos"> 18</span><span class="c1">// This example showcases various ways to work with Datasets. It's</span> |
| <span class="linenos"> 19</span><span class="c1">// intended to be paired with the documentation.</span> |
| <span class="linenos"> 20</span> |
| <span class="linenos"> 21</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><arrow/api.h></span> |
| <span class="linenos"> 22</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><arrow/compute/cast.h></span> |
| <span class="linenos"> 23</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><arrow/dataset/dataset.h></span> |
| <span class="linenos"> 24</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><arrow/dataset/discovery.h></span> |
| <span class="linenos"> 25</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><arrow/dataset/file_base.h></span> |
| <span class="linenos"> 26</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><arrow/dataset/file_ipc.h></span> |
| <span class="linenos"> 27</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><arrow/dataset/file_parquet.h></span> |
| <span class="linenos"> 28</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><arrow/dataset/scanner.h></span> |
| <span class="linenos"> 29</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><arrow/filesystem/filesystem.h></span> |
| <span class="linenos"> 30</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><arrow/ipc/writer.h></span> |
| <span class="linenos"> 31</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><arrow/util/iterator.h></span> |
| <span class="linenos"> 32</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><parquet/arrow/writer.h></span> |
| <span class="linenos"> 33</span><span class="cp">#include</span><span class="w"> </span><span class="cpf">"arrow/compute/expression.h"</span> |
| <span class="linenos"> 34</span> |
| <span class="linenos"> 35</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><iostream></span> |
| <span class="linenos"> 36</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><vector></span> |
| <span class="linenos"> 37</span> |
| <span class="linenos"> 38</span><span class="k">namespace</span><span class="w"> </span><span class="nn">ds</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nn">arrow</span><span class="o">::</span><span class="nn">dataset</span><span class="p">;</span> |
| <span class="linenos"> 39</span><span class="k">namespace</span><span class="w"> </span><span class="nn">fs</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nn">arrow</span><span class="o">::</span><span class="nn">fs</span><span class="p">;</span> |
| <span class="linenos"> 40</span><span class="k">namespace</span><span class="w"> </span><span class="nn">cp</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nn">arrow</span><span class="o">::</span><span class="nn">compute</span><span class="p">;</span> |
| <span class="linenos"> 41</span> |
| <span class="linenos"> 42</span><span class="cm">/**</span> |
| <span class="linenos"> 43</span><span class="cm"> * \brief Run Example</span> |
| <span class="linenos"> 44</span><span class="cm"> *</span> |
| <span class="linenos"> 45</span><span class="cm"> * ./debug/dataset-documentation-example file:///<some_path>/<some_directory> parquet</span> |
| <span class="linenos"> 46</span><span class="cm"> */</span> |
| <span class="linenos"> 47</span> |
| <span class="linenos"> 48</span><span class="c1">// (Doc section: Reading Datasets)</span> |
| <span class="linenos"> 49</span><span class="c1">// Generate some data for the rest of this example.</span> |
| <span class="linenos"> 50</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">>></span><span class="w"> </span><span class="n">CreateTable</span><span class="p">()</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos"> 51</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">schema</span><span class="w"> </span><span class="o">=</span> |
| <span class="linenos"> 52</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">schema</span><span class="p">({</span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">int64</span><span class="p">()),</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"b"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">int64</span><span class="p">()),</span> |
| <span class="linenos"> 53</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"c"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">int64</span><span class="p">())});</span> |
| <span class="linenos"> 54</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Array</span><span class="o">></span><span class="w"> </span><span class="n">array_a</span><span class="p">;</span> |
| <span class="linenos"> 55</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Array</span><span class="o">></span><span class="w"> </span><span class="n">array_b</span><span class="p">;</span> |
| <span class="linenos"> 56</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Array</span><span class="o">></span><span class="w"> </span><span class="n">array_c</span><span class="p">;</span> |
| <span class="linenos"> 57</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">NumericBuilder</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Int64Type</span><span class="o">></span><span class="w"> </span><span class="n">builder</span><span class="p">;</span> |
| <span class="linenos"> 58</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">({</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">9</span><span class="p">}));</span> |
| <span class="linenos"> 59</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">(</span><span class="o">&</span><span class="n">array_a</span><span class="p">));</span> |
| <span class="linenos"> 60</span><span class="w"> </span><span class="n">builder</span><span class="p">.</span><span class="n">Reset</span><span class="p">();</span> |
| <span class="linenos"> 61</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">({</span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">}));</span> |
| <span class="linenos"> 62</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">(</span><span class="o">&</span><span class="n">array_b</span><span class="p">));</span> |
| <span class="linenos"> 63</span><span class="w"> </span><span class="n">builder</span><span class="p">.</span><span class="n">Reset</span><span class="p">();</span> |
| <span class="linenos"> 64</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">({</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">}));</span> |
| <span class="linenos"> 65</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">(</span><span class="o">&</span><span class="n">array_c</span><span class="p">));</span> |
| <span class="linenos"> 66</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span><span class="n">schema</span><span class="p">,</span><span class="w"> </span><span class="p">{</span><span class="n">array_a</span><span class="p">,</span><span class="w"> </span><span class="n">array_b</span><span class="p">,</span><span class="w"> </span><span class="n">array_c</span><span class="p">});</span> |
| <span class="linenos"> 67</span><span class="p">}</span> |
| <span class="linenos"> 68</span> |
| <span class="linenos"> 69</span><span class="c1">// Set up a dataset by writing two Parquet files.</span> |
| <span class="linenos"> 70</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span><span class="w"> </span><span class="n">CreateExampleParquetDataset</span><span class="p">(</span> |
| <span class="linenos"> 71</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">root_path</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos"> 72</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">base_path</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">root_path</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">"/parquet_dataset"</span><span class="p">;</span> |
| <span class="linenos"> 73</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">filesystem</span><span class="o">-></span><span class="n">CreateDir</span><span class="p">(</span><span class="n">base_path</span><span class="p">));</span> |
| <span class="linenos"> 74</span><span class="w"> </span><span class="c1">// Create an Arrow Table</span> |
| <span class="linenos"> 75</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">table</span><span class="p">,</span><span class="w"> </span><span class="n">CreateTable</span><span class="p">());</span> |
| <span class="linenos"> 76</span><span class="w"> </span><span class="c1">// Write it into two Parquet files</span> |
| <span class="linenos"> 77</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">output</span><span class="p">,</span> |
| <span class="linenos"> 78</span><span class="w"> </span><span class="n">filesystem</span><span class="o">-></span><span class="n">OpenOutputStream</span><span class="p">(</span><span class="n">base_path</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">"/data1.parquet"</span><span class="p">));</span> |
| <span class="linenos"> 79</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">parquet</span><span class="o">::</span><span class="n">arrow</span><span class="o">::</span><span class="n">WriteTable</span><span class="p">(</span> |
| <span class="linenos"> 80</span><span class="w"> </span><span class="o">*</span><span class="n">table</span><span class="o">-></span><span class="n">Slice</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">),</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">default_memory_pool</span><span class="p">(),</span><span class="w"> </span><span class="n">output</span><span class="p">,</span><span class="w"> </span><span class="cm">/*chunk_size=*/</span><span class="mi">2048</span><span class="p">));</span> |
| <span class="linenos"> 81</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">output</span><span class="p">,</span> |
| <span class="linenos"> 82</span><span class="w"> </span><span class="n">filesystem</span><span class="o">-></span><span class="n">OpenOutputStream</span><span class="p">(</span><span class="n">base_path</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">"/data2.parquet"</span><span class="p">));</span> |
| <span class="linenos"> 83</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">parquet</span><span class="o">::</span><span class="n">arrow</span><span class="o">::</span><span class="n">WriteTable</span><span class="p">(</span> |
| <span class="linenos"> 84</span><span class="w"> </span><span class="o">*</span><span class="n">table</span><span class="o">-></span><span class="n">Slice</span><span class="p">(</span><span class="mi">5</span><span class="p">),</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">default_memory_pool</span><span class="p">(),</span><span class="w"> </span><span class="n">output</span><span class="p">,</span><span class="w"> </span><span class="cm">/*chunk_size=*/</span><span class="mi">2048</span><span class="p">));</span> |
| <span class="linenos"> 85</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">base_path</span><span class="p">;</span> |
| <span class="linenos"> 86</span><span class="p">}</span> |
| <span class="linenos"> 87</span><span class="c1">// (Doc section: Reading Datasets)</span> |
| <span class="linenos"> 88</span> |
| <span class="linenos"> 89</span><span class="c1">// (Doc section: Reading different file formats)</span> |
| <span class="linenos"> 90</span><span class="c1">// Set up a dataset by writing two Feather files.</span> |
| <span class="linenos"> 91</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span><span class="w"> </span><span class="n">CreateExampleFeatherDataset</span><span class="p">(</span> |
| <span class="linenos"> 92</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">root_path</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos"> 93</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">base_path</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">root_path</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">"/feather_dataset"</span><span class="p">;</span> |
| <span class="linenos"> 94</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">filesystem</span><span class="o">-></span><span class="n">CreateDir</span><span class="p">(</span><span class="n">base_path</span><span class="p">));</span> |
| <span class="linenos"> 95</span><span class="w"> </span><span class="c1">// Create an Arrow Table</span> |
| <span class="linenos"> 96</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">table</span><span class="p">,</span><span class="w"> </span><span class="n">CreateTable</span><span class="p">());</span> |
| <span class="linenos"> 97</span><span class="w"> </span><span class="c1">// Write it into two Feather files</span> |
| <span class="linenos"> 98</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">output</span><span class="p">,</span> |
| <span class="linenos"> 99</span><span class="w"> </span><span class="n">filesystem</span><span class="o">-></span><span class="n">OpenOutputStream</span><span class="p">(</span><span class="n">base_path</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">"/data1.feather"</span><span class="p">));</span> |
| <span class="linenos">100</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">writer</span><span class="p">,</span> |
| <span class="linenos">101</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">ipc</span><span class="o">::</span><span class="n">MakeFileWriter</span><span class="p">(</span><span class="n">output</span><span class="p">.</span><span class="n">get</span><span class="p">(),</span><span class="w"> </span><span class="n">table</span><span class="o">-></span><span class="n">schema</span><span class="p">()));</span> |
| <span class="linenos">102</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">writer</span><span class="o">-></span><span class="n">WriteTable</span><span class="p">(</span><span class="o">*</span><span class="n">table</span><span class="o">-></span><span class="n">Slice</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">)));</span> |
| <span class="linenos">103</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">writer</span><span class="o">-></span><span class="n">Close</span><span class="p">());</span> |
| <span class="linenos">104</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">output</span><span class="p">,</span> |
| <span class="linenos">105</span><span class="w"> </span><span class="n">filesystem</span><span class="o">-></span><span class="n">OpenOutputStream</span><span class="p">(</span><span class="n">base_path</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">"/data2.feather"</span><span class="p">));</span> |
| <span class="linenos">106</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">writer</span><span class="p">,</span> |
| <span class="linenos">107</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">ipc</span><span class="o">::</span><span class="n">MakeFileWriter</span><span class="p">(</span><span class="n">output</span><span class="p">.</span><span class="n">get</span><span class="p">(),</span><span class="w"> </span><span class="n">table</span><span class="o">-></span><span class="n">schema</span><span class="p">()));</span> |
| <span class="linenos">108</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">writer</span><span class="o">-></span><span class="n">WriteTable</span><span class="p">(</span><span class="o">*</span><span class="n">table</span><span class="o">-></span><span class="n">Slice</span><span class="p">(</span><span class="mi">5</span><span class="p">)));</span> |
| <span class="linenos">109</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">writer</span><span class="o">-></span><span class="n">Close</span><span class="p">());</span> |
| <span class="linenos">110</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">base_path</span><span class="p">;</span> |
| <span class="linenos">111</span><span class="p">}</span> |
| <span class="linenos">112</span><span class="c1">// (Doc section: Reading different file formats)</span> |
| <span class="linenos">113</span> |
| <span class="linenos">114</span><span class="c1">// (Doc section: Reading and writing partitioned data)</span> |
| <span class="linenos">115</span><span class="c1">// Set up a dataset by writing files with partitioning</span> |
| <span class="linenos">116</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span><span class="w"> </span><span class="n">CreateExampleParquetHivePartitionedDataset</span><span class="p">(</span> |
| <span class="linenos">117</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">root_path</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">118</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">base_path</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">root_path</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="s">"/parquet_dataset"</span><span class="p">;</span> |
| <span class="linenos">119</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">filesystem</span><span class="o">-></span><span class="n">CreateDir</span><span class="p">(</span><span class="n">base_path</span><span class="p">));</span> |
| <span class="linenos">120</span><span class="w"> </span><span class="c1">// Create an Arrow Table</span> |
| <span class="linenos">121</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">schema</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">schema</span><span class="p">(</span> |
| <span class="linenos">122</span><span class="w"> </span><span class="p">{</span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">int64</span><span class="p">()),</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"b"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">int64</span><span class="p">()),</span> |
| <span class="linenos">123</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"c"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">int64</span><span class="p">()),</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"part"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">utf8</span><span class="p">())});</span> |
| <span class="linenos">124</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Array</span><span class="o">>></span><span class="w"> </span><span class="n">arrays</span><span class="p">(</span><span class="mi">4</span><span class="p">);</span> |
| <span class="linenos">125</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">NumericBuilder</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Int64Type</span><span class="o">></span><span class="w"> </span><span class="n">builder</span><span class="p">;</span> |
| <span class="linenos">126</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">({</span><span class="mi">0</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">9</span><span class="p">}));</span> |
| <span class="linenos">127</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">(</span><span class="o">&</span><span class="n">arrays</span><span class="p">[</span><span class="mi">0</span><span class="p">]));</span> |
| <span class="linenos">128</span><span class="w"> </span><span class="n">builder</span><span class="p">.</span><span class="n">Reset</span><span class="p">();</span> |
| <span class="linenos">129</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">({</span><span class="mi">9</span><span class="p">,</span><span class="w"> </span><span class="mi">8</span><span class="p">,</span><span class="w"> </span><span class="mi">7</span><span class="p">,</span><span class="w"> </span><span class="mi">6</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">,</span><span class="w"> </span><span class="mi">4</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">0</span><span class="p">}));</span> |
| <span class="linenos">130</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">(</span><span class="o">&</span><span class="n">arrays</span><span class="p">[</span><span class="mi">1</span><span class="p">]));</span> |
| <span class="linenos">131</span><span class="w"> </span><span class="n">builder</span><span class="p">.</span><span class="n">Reset</span><span class="p">();</span> |
| <span class="linenos">132</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">({</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">}));</span> |
| <span class="linenos">133</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">(</span><span class="o">&</span><span class="n">arrays</span><span class="p">[</span><span class="mi">2</span><span class="p">]));</span> |
| <span class="linenos">134</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">StringBuilder</span><span class="w"> </span><span class="n">string_builder</span><span class="p">;</span> |
| <span class="linenos">135</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span> |
| <span class="linenos">136</span><span class="w"> </span><span class="n">string_builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">({</span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="s">"a"</span><span class="p">,</span><span class="w"> </span><span class="s">"b"</span><span class="p">,</span><span class="w"> </span><span class="s">"b"</span><span class="p">,</span><span class="w"> </span><span class="s">"b"</span><span class="p">,</span><span class="w"> </span><span class="s">"b"</span><span class="p">,</span><span class="w"> </span><span class="s">"b"</span><span class="p">}));</span> |
| <span class="linenos">137</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">string_builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">(</span><span class="o">&</span><span class="n">arrays</span><span class="p">[</span><span class="mi">3</span><span class="p">]));</span> |
| <span class="linenos">138</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">table</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span><span class="n">schema</span><span class="p">,</span><span class="w"> </span><span class="n">arrays</span><span class="p">);</span> |
| <span class="linenos">139</span><span class="w"> </span><span class="c1">// Write it using Datasets</span> |
| <span class="linenos">140</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">dataset</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">InMemoryDataset</span><span class="o">></span><span class="p">(</span><span class="n">table</span><span class="p">);</span> |
| <span class="linenos">141</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner_builder</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">NewScan</span><span class="p">());</span> |
| <span class="linenos">142</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner</span><span class="p">,</span><span class="w"> </span><span class="n">scanner_builder</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">143</span> |
| <span class="linenos">144</span><span class="w"> </span><span class="c1">// The partition schema determines which fields are part of the partitioning.</span> |
| <span class="linenos">145</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">partition_schema</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">schema</span><span class="p">({</span><span class="n">arrow</span><span class="o">::</span><span class="n">field</span><span class="p">(</span><span class="s">"part"</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">utf8</span><span class="p">())});</span> |
| <span class="linenos">146</span><span class="w"> </span><span class="c1">// We'll use Hive-style partitioning, which creates directories with "key=value" pairs.</span> |
| <span class="linenos">147</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">partitioning</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">HivePartitioning</span><span class="o">></span><span class="p">(</span><span class="n">partition_schema</span><span class="p">);</span> |
| <span class="linenos">148</span><span class="w"> </span><span class="c1">// We'll write Parquet files.</span> |
| <span class="linenos">149</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">format</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">ParquetFileFormat</span><span class="o">></span><span class="p">();</span> |
| <span class="linenos">150</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDatasetWriteOptions</span><span class="w"> </span><span class="n">write_options</span><span class="p">;</span> |
| <span class="linenos">151</span><span class="w"> </span><span class="n">write_options</span><span class="p">.</span><span class="n">file_write_options</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">format</span><span class="o">-></span><span class="n">DefaultWriteOptions</span><span class="p">();</span> |
| <span class="linenos">152</span><span class="w"> </span><span class="n">write_options</span><span class="p">.</span><span class="n">filesystem</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">filesystem</span><span class="p">;</span> |
| <span class="linenos">153</span><span class="w"> </span><span class="n">write_options</span><span class="p">.</span><span class="n">base_dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">base_path</span><span class="p">;</span> |
| <span class="linenos">154</span><span class="w"> </span><span class="n">write_options</span><span class="p">.</span><span class="n">partitioning</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">partitioning</span><span class="p">;</span> |
| <span class="linenos">155</span><span class="w"> </span><span class="n">write_options</span><span class="p">.</span><span class="n">basename_template</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"part{i}.parquet"</span><span class="p">;</span> |
| <span class="linenos">156</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDataset</span><span class="o">::</span><span class="n">Write</span><span class="p">(</span><span class="n">write_options</span><span class="p">,</span><span class="w"> </span><span class="n">scanner</span><span class="p">));</span> |
| <span class="linenos">157</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">base_path</span><span class="p">;</span> |
| <span class="linenos">158</span><span class="p">}</span> |
| <span class="linenos">159</span><span class="c1">// (Doc section: Reading and writing partitioned data)</span> |
| <span class="linenos">160</span> |
| <span class="linenos">161</span><span class="c1">// (Doc section: Dataset discovery)</span> |
| <span class="linenos">162</span><span class="c1">// Read the whole dataset with the given format, without partitioning.</span> |
| <span class="linenos">163</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">>></span><span class="w"> </span><span class="n">ScanWholeDataset</span><span class="p">(</span> |
| <span class="linenos">164</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span> |
| <span class="linenos">165</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">FileFormat</span><span class="o">>&</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">base_dir</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">166</span><span class="w"> </span><span class="c1">// Create a dataset by scanning the filesystem for files</span> |
| <span class="linenos">167</span><span class="w"> </span><span class="n">fs</span><span class="o">::</span><span class="n">FileSelector</span><span class="w"> </span><span class="n">selector</span><span class="p">;</span> |
| <span class="linenos">168</span><span class="w"> </span><span class="n">selector</span><span class="p">.</span><span class="n">base_dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">base_dir</span><span class="p">;</span> |
| <span class="linenos">169</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span> |
| <span class="linenos">170</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">factory</span><span class="p">,</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDatasetFactory</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="n">selector</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span> |
| <span class="linenos">171</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemFactoryOptions</span><span class="p">()));</span> |
| <span class="linenos">172</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">dataset</span><span class="p">,</span><span class="w"> </span><span class="n">factory</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">173</span><span class="w"> </span><span class="c1">// Print out the fragments</span> |
| <span class="linenos">174</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">fragments</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">GetFragments</span><span class="p">())</span> |
| <span class="linenos">175</span><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="k">auto</span><span class="o">&</span><span class="w"> </span><span class="n">fragment</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">fragments</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">176</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"Found fragment: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">fragment</span><span class="p">)</span><span class="o">-></span><span class="n">ToString</span><span class="p">()</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> |
| <span class="linenos">177</span><span class="w"> </span><span class="p">}</span> |
| <span class="linenos">178</span><span class="w"> </span><span class="c1">// Read the entire dataset as a Table</span> |
| <span class="linenos">179</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scan_builder</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">NewScan</span><span class="p">());</span> |
| <span class="linenos">180</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner</span><span class="p">,</span><span class="w"> </span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">181</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">scanner</span><span class="o">-></span><span class="n">ToTable</span><span class="p">();</span> |
| <span class="linenos">182</span><span class="p">}</span> |
| <span class="linenos">183</span><span class="c1">// (Doc section: Dataset discovery)</span> |
| <span class="linenos">184</span> |
| <span class="linenos">185</span><span class="c1">// (Doc section: Filtering data)</span> |
| <span class="linenos">186</span><span class="c1">// Read a dataset, but select only column "b" and only rows where b < 4.</span> |
| <span class="linenos">187</span><span class="c1">//</span> |
| <span class="linenos">188</span><span class="c1">// This is useful when you only want a few columns from a dataset. Where possible,</span> |
| <span class="linenos">189</span><span class="c1">// Datasets will push down the column selection such that less work is done.</span> |
| <span class="linenos">190</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">>></span><span class="w"> </span><span class="n">FilterAndSelectDataset</span><span class="p">(</span> |
| <span class="linenos">191</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span> |
| <span class="linenos">192</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">FileFormat</span><span class="o">>&</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">base_dir</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">193</span><span class="w"> </span><span class="n">fs</span><span class="o">::</span><span class="n">FileSelector</span><span class="w"> </span><span class="n">selector</span><span class="p">;</span> |
| <span class="linenos">194</span><span class="w"> </span><span class="n">selector</span><span class="p">.</span><span class="n">base_dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">base_dir</span><span class="p">;</span> |
| <span class="linenos">195</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span> |
| <span class="linenos">196</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">factory</span><span class="p">,</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDatasetFactory</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="n">selector</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span> |
| <span class="linenos">197</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemFactoryOptions</span><span class="p">()));</span> |
| <span class="linenos">198</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">dataset</span><span class="p">,</span><span class="w"> </span><span class="n">factory</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">199</span><span class="w"> </span><span class="c1">// Read specified columns with a row filter</span> |
| <span class="linenos">200</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scan_builder</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">NewScan</span><span class="p">());</span> |
| <span class="linenos">201</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Project</span><span class="p">({</span><span class="s">"b"</span><span class="p">}));</span> |
| <span class="linenos">202</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Filter</span><span class="p">(</span><span class="n">cp</span><span class="o">::</span><span class="n">less</span><span class="p">(</span><span class="n">cp</span><span class="o">::</span><span class="n">field_ref</span><span class="p">(</span><span class="s">"b"</span><span class="p">),</span><span class="w"> </span><span class="n">cp</span><span class="o">::</span><span class="n">literal</span><span class="p">(</span><span class="mi">4</span><span class="p">))));</span> |
| <span class="linenos">203</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner</span><span class="p">,</span><span class="w"> </span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">204</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">scanner</span><span class="o">-></span><span class="n">ToTable</span><span class="p">();</span> |
| <span class="linenos">205</span><span class="p">}</span> |
| <span class="linenos">206</span><span class="c1">// (Doc section: Filtering data)</span> |
| <span class="linenos">207</span> |
| <span class="linenos">208</span><span class="c1">// (Doc section: Projecting columns)</span> |
| <span class="linenos">209</span><span class="c1">// Read a dataset, but with column projection.</span> |
| <span class="linenos">210</span><span class="c1">//</span> |
| <span class="linenos">211</span><span class="c1">// This is useful to derive new columns from existing data. For example, here we</span> |
| <span class="linenos">212</span><span class="c1">// demonstrate casting a column to a different type, and turning a numeric column into a</span> |
| <span class="linenos">213</span><span class="c1">// boolean column based on a predicate. You could also rename columns or perform</span> |
| <span class="linenos">214</span><span class="c1">// computations involving multiple columns.</span> |
| <span class="linenos">215</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">>></span><span class="w"> </span><span class="n">ProjectDataset</span><span class="p">(</span> |
| <span class="linenos">216</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span> |
| <span class="linenos">217</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">FileFormat</span><span class="o">>&</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">base_dir</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">218</span><span class="w"> </span><span class="n">fs</span><span class="o">::</span><span class="n">FileSelector</span><span class="w"> </span><span class="n">selector</span><span class="p">;</span> |
| <span class="linenos">219</span><span class="w"> </span><span class="n">selector</span><span class="p">.</span><span class="n">base_dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">base_dir</span><span class="p">;</span> |
| <span class="linenos">220</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span> |
| <span class="linenos">221</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">factory</span><span class="p">,</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDatasetFactory</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="n">selector</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span> |
| <span class="linenos">222</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemFactoryOptions</span><span class="p">()));</span> |
| <span class="linenos">223</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">dataset</span><span class="p">,</span><span class="w"> </span><span class="n">factory</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">224</span><span class="w"> </span><span class="c1">// Read specified columns with a row filter</span> |
| <span class="linenos">225</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scan_builder</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">NewScan</span><span class="p">());</span> |
| <span class="linenos">226</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Project</span><span class="p">(</span> |
| <span class="linenos">227</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">228</span><span class="w"> </span><span class="c1">// Leave column "a" as-is.</span> |
| <span class="linenos">229</span><span class="w"> </span><span class="n">cp</span><span class="o">::</span><span class="n">field_ref</span><span class="p">(</span><span class="s">"a"</span><span class="p">),</span> |
| <span class="linenos">230</span><span class="w"> </span><span class="c1">// Cast column "b" to float32.</span> |
| <span class="linenos">231</span><span class="w"> </span><span class="n">cp</span><span class="o">::</span><span class="n">call</span><span class="p">(</span><span class="s">"cast"</span><span class="p">,</span><span class="w"> </span><span class="p">{</span><span class="n">cp</span><span class="o">::</span><span class="n">field_ref</span><span class="p">(</span><span class="s">"b"</span><span class="p">)},</span> |
| <span class="linenos">232</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">compute</span><span class="o">::</span><span class="n">CastOptions</span><span class="o">::</span><span class="n">Safe</span><span class="p">(</span><span class="n">arrow</span><span class="o">::</span><span class="n">float32</span><span class="p">())),</span> |
| <span class="linenos">233</span><span class="w"> </span><span class="c1">// Derive a boolean column from "c".</span> |
| <span class="linenos">234</span><span class="w"> </span><span class="n">cp</span><span class="o">::</span><span class="n">equal</span><span class="p">(</span><span class="n">cp</span><span class="o">::</span><span class="n">field_ref</span><span class="p">(</span><span class="s">"c"</span><span class="p">),</span><span class="w"> </span><span class="n">cp</span><span class="o">::</span><span class="n">literal</span><span class="p">(</span><span class="mi">1</span><span class="p">)),</span> |
| <span class="linenos">235</span><span class="w"> </span><span class="p">},</span> |
| <span class="linenos">236</span><span class="w"> </span><span class="p">{</span><span class="s">"a_renamed"</span><span class="p">,</span><span class="w"> </span><span class="s">"b_as_float32"</span><span class="p">,</span><span class="w"> </span><span class="s">"c_1"</span><span class="p">}));</span> |
| <span class="linenos">237</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner</span><span class="p">,</span><span class="w"> </span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">238</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">scanner</span><span class="o">-></span><span class="n">ToTable</span><span class="p">();</span> |
| <span class="linenos">239</span><span class="p">}</span> |
| <span class="linenos">240</span><span class="c1">// (Doc section: Projecting columns)</span> |
| <span class="linenos">241</span> |
| <span class="linenos">242</span><span class="c1">// (Doc section: Projecting columns #2)</span> |
| <span class="linenos">243</span><span class="c1">// Read a dataset, but with column projection.</span> |
| <span class="linenos">244</span><span class="c1">//</span> |
| <span class="linenos">245</span><span class="c1">// This time, we read all original columns plus one derived column. This simply combines</span> |
| <span class="linenos">246</span><span class="c1">// the previous two examples: selecting a subset of columns by name, and deriving new</span> |
| <span class="linenos">247</span><span class="c1">// columns with an expression.</span> |
| <span class="linenos">248</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">>></span><span class="w"> </span><span class="n">SelectAndProjectDataset</span><span class="p">(</span> |
| <span class="linenos">249</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span> |
| <span class="linenos">250</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">FileFormat</span><span class="o">>&</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">base_dir</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">251</span><span class="w"> </span><span class="n">fs</span><span class="o">::</span><span class="n">FileSelector</span><span class="w"> </span><span class="n">selector</span><span class="p">;</span> |
| <span class="linenos">252</span><span class="w"> </span><span class="n">selector</span><span class="p">.</span><span class="n">base_dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">base_dir</span><span class="p">;</span> |
| <span class="linenos">253</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span> |
| <span class="linenos">254</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">factory</span><span class="p">,</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDatasetFactory</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="n">selector</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span> |
| <span class="linenos">255</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemFactoryOptions</span><span class="p">()));</span> |
| <span class="linenos">256</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">dataset</span><span class="p">,</span><span class="w"> </span><span class="n">factory</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">257</span><span class="w"> </span><span class="c1">// Read specified columns with a row filter</span> |
| <span class="linenos">258</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scan_builder</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">NewScan</span><span class="p">());</span> |
| <span class="linenos">259</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span><span class="w"> </span><span class="n">names</span><span class="p">;</span> |
| <span class="linenos">260</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">cp</span><span class="o">::</span><span class="n">Expression</span><span class="o">></span><span class="w"> </span><span class="n">exprs</span><span class="p">;</span> |
| <span class="linenos">261</span><span class="w"> </span><span class="c1">// Read all the original columns.</span> |
| <span class="linenos">262</span><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="k">auto</span><span class="o">&</span><span class="w"> </span><span class="n">field</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">schema</span><span class="p">()</span><span class="o">-></span><span class="n">fields</span><span class="p">())</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">263</span><span class="w"> </span><span class="n">names</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">field</span><span class="o">-></span><span class="n">name</span><span class="p">());</span> |
| <span class="linenos">264</span><span class="w"> </span><span class="n">exprs</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">cp</span><span class="o">::</span><span class="n">field_ref</span><span class="p">(</span><span class="n">field</span><span class="o">-></span><span class="n">name</span><span class="p">()));</span> |
| <span class="linenos">265</span><span class="w"> </span><span class="p">}</span> |
| <span class="linenos">266</span><span class="w"> </span><span class="c1">// Also derive a new column.</span> |
| <span class="linenos">267</span><span class="w"> </span><span class="n">names</span><span class="p">.</span><span class="n">emplace_back</span><span class="p">(</span><span class="s">"b_large"</span><span class="p">);</span> |
| <span class="linenos">268</span><span class="w"> </span><span class="n">exprs</span><span class="p">.</span><span class="n">push_back</span><span class="p">(</span><span class="n">cp</span><span class="o">::</span><span class="n">greater</span><span class="p">(</span><span class="n">cp</span><span class="o">::</span><span class="n">field_ref</span><span class="p">(</span><span class="s">"b"</span><span class="p">),</span><span class="w"> </span><span class="n">cp</span><span class="o">::</span><span class="n">literal</span><span class="p">(</span><span class="mi">1</span><span class="p">)));</span> |
| <span class="linenos">269</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Project</span><span class="p">(</span><span class="n">exprs</span><span class="p">,</span><span class="w"> </span><span class="n">names</span><span class="p">));</span> |
| <span class="linenos">270</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner</span><span class="p">,</span><span class="w"> </span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">271</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">scanner</span><span class="o">-></span><span class="n">ToTable</span><span class="p">();</span> |
| <span class="linenos">272</span><span class="p">}</span> |
| <span class="linenos">273</span><span class="c1">// (Doc section: Projecting columns #2)</span> |
| <span class="linenos">274</span> |
| <span class="linenos">275</span><span class="c1">// (Doc section: Reading and writing partitioned data #2)</span> |
| <span class="linenos">276</span><span class="c1">// Read an entire dataset, but with partitioning information.</span> |
| <span class="linenos">277</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">>></span><span class="w"> </span><span class="n">ScanPartitionedDataset</span><span class="p">(</span> |
| <span class="linenos">278</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span> |
| <span class="linenos">279</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">FileFormat</span><span class="o">>&</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">base_dir</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">280</span><span class="w"> </span><span class="n">fs</span><span class="o">::</span><span class="n">FileSelector</span><span class="w"> </span><span class="n">selector</span><span class="p">;</span> |
| <span class="linenos">281</span><span class="w"> </span><span class="n">selector</span><span class="p">.</span><span class="n">base_dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">base_dir</span><span class="p">;</span> |
| <span class="linenos">282</span><span class="w"> </span><span class="n">selector</span><span class="p">.</span><span class="n">recursive</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">true</span><span class="p">;</span><span class="w"> </span><span class="c1">// Make sure to search subdirectories</span> |
| <span class="linenos">283</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemFactoryOptions</span><span class="w"> </span><span class="n">options</span><span class="p">;</span> |
| <span class="linenos">284</span><span class="w"> </span><span class="c1">// We'll use Hive-style partitioning. We'll let Arrow Datasets infer the partition</span> |
| <span class="linenos">285</span><span class="w"> </span><span class="c1">// schema.</span> |
| <span class="linenos">286</span><span class="w"> </span><span class="n">options</span><span class="p">.</span><span class="n">partitioning</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">HivePartitioning</span><span class="o">::</span><span class="n">MakeFactory</span><span class="p">();</span> |
| <span class="linenos">287</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">factory</span><span class="p">,</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDatasetFactory</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span> |
| <span class="linenos">288</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="n">selector</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="n">options</span><span class="p">));</span> |
| <span class="linenos">289</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">dataset</span><span class="p">,</span><span class="w"> </span><span class="n">factory</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">290</span><span class="w"> </span><span class="c1">// Print out the fragments</span> |
| <span class="linenos">291</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">fragments</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">GetFragments</span><span class="p">());</span> |
| <span class="linenos">292</span><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="k">auto</span><span class="o">&</span><span class="w"> </span><span class="n">fragment</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">fragments</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">293</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"Found fragment: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">fragment</span><span class="p">)</span><span class="o">-></span><span class="n">ToString</span><span class="p">()</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> |
| <span class="linenos">294</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"Partition expression: "</span> |
| <span class="linenos">295</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="p">(</span><span class="o">*</span><span class="n">fragment</span><span class="p">)</span><span class="o">-></span><span class="n">partition_expression</span><span class="p">().</span><span class="n">ToString</span><span class="p">()</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> |
| <span class="linenos">296</span><span class="w"> </span><span class="p">}</span> |
| <span class="linenos">297</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scan_builder</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">NewScan</span><span class="p">());</span> |
| <span class="linenos">298</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner</span><span class="p">,</span><span class="w"> </span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">299</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">scanner</span><span class="o">-></span><span class="n">ToTable</span><span class="p">();</span> |
| <span class="linenos">300</span><span class="p">}</span> |
| <span class="linenos">301</span><span class="c1">// (Doc section: Reading and writing partitioned data #2)</span> |
| <span class="linenos">302</span> |
| <span class="linenos">303</span><span class="c1">// (Doc section: Reading and writing partitioned data #3)</span> |
| <span class="linenos">304</span><span class="c1">// Read an entire dataset, but with partitioning information. Also, filter the dataset on</span> |
| <span class="linenos">305</span><span class="c1">// the partition values.</span> |
| <span class="linenos">306</span><span class="n">arrow</span><span class="o">::</span><span class="n">Result</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">>></span><span class="w"> </span><span class="n">FilterPartitionedDataset</span><span class="p">(</span> |
| <span class="linenos">307</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystem</span><span class="o">>&</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span> |
| <span class="linenos">308</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">FileFormat</span><span class="o">>&</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">base_dir</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">309</span><span class="w"> </span><span class="n">fs</span><span class="o">::</span><span class="n">FileSelector</span><span class="w"> </span><span class="n">selector</span><span class="p">;</span> |
| <span class="linenos">310</span><span class="w"> </span><span class="n">selector</span><span class="p">.</span><span class="n">base_dir</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">base_dir</span><span class="p">;</span> |
| <span class="linenos">311</span><span class="w"> </span><span class="n">selector</span><span class="p">.</span><span class="n">recursive</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">true</span><span class="p">;</span> |
| <span class="linenos">312</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemFactoryOptions</span><span class="w"> </span><span class="n">options</span><span class="p">;</span> |
| <span class="linenos">313</span><span class="w"> </span><span class="n">options</span><span class="p">.</span><span class="n">partitioning</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">HivePartitioning</span><span class="o">::</span><span class="n">MakeFactory</span><span class="p">();</span> |
| <span class="linenos">314</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">factory</span><span class="p">,</span><span class="w"> </span><span class="n">ds</span><span class="o">::</span><span class="n">FileSystemDatasetFactory</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span> |
| <span class="linenos">315</span><span class="w"> </span><span class="n">filesystem</span><span class="p">,</span><span class="w"> </span><span class="n">selector</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="n">options</span><span class="p">));</span> |
| <span class="linenos">316</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">dataset</span><span class="p">,</span><span class="w"> </span><span class="n">factory</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">317</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scan_builder</span><span class="p">,</span><span class="w"> </span><span class="n">dataset</span><span class="o">-></span><span class="n">NewScan</span><span class="p">());</span> |
| <span class="linenos">318</span><span class="w"> </span><span class="c1">// Filter based on the partition values. This will mean that we won't even read the</span> |
| <span class="linenos">319</span><span class="w"> </span><span class="c1">// files whose partition expressions don't match the filter.</span> |
| <span class="linenos">320</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span> |
| <span class="linenos">321</span><span class="w"> </span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Filter</span><span class="p">(</span><span class="n">cp</span><span class="o">::</span><span class="n">equal</span><span class="p">(</span><span class="n">cp</span><span class="o">::</span><span class="n">field_ref</span><span class="p">(</span><span class="s">"part"</span><span class="p">),</span><span class="w"> </span><span class="n">cp</span><span class="o">::</span><span class="n">literal</span><span class="p">(</span><span class="s">"b"</span><span class="p">))));</span> |
| <span class="linenos">322</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">scanner</span><span class="p">,</span><span class="w"> </span><span class="n">scan_builder</span><span class="o">-></span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos">323</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">scanner</span><span class="o">-></span><span class="n">ToTable</span><span class="p">();</span> |
| <span class="linenos">324</span><span class="p">}</span> |
| <span class="linenos">325</span><span class="c1">// (Doc section: Reading and writing partitioned data #3)</span> |
| <span class="linenos">326</span> |
| <span class="linenos">327</span><span class="n">arrow</span><span class="o">::</span><span class="n">Status</span><span class="w"> </span><span class="n">RunDatasetDocumentation</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">format_name</span><span class="p">,</span> |
| <span class="linenos">328</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">uri</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span><span class="w"> </span><span class="n">mode</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">329</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="w"> </span><span class="n">base_path</span><span class="p">;</span> |
| <span class="linenos">330</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">FileFormat</span><span class="o">></span><span class="w"> </span><span class="n">format</span><span class="p">;</span> |
| <span class="linenos">331</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="w"> </span><span class="n">root_path</span><span class="p">;</span> |
| <span class="linenos">332</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">fs</span><span class="p">,</span><span class="w"> </span><span class="n">fs</span><span class="o">::</span><span class="n">FileSystemFromUri</span><span class="p">(</span><span class="n">uri</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">root_path</span><span class="p">));</span> |
| <span class="linenos">333</span> |
| <span class="linenos">334</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">format_name</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="s">"feather"</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">335</span><span class="w"> </span><span class="n">format</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">IpcFileFormat</span><span class="o">></span><span class="p">();</span> |
| <span class="linenos">336</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">base_path</span><span class="p">,</span><span class="w"> </span><span class="n">CreateExampleFeatherDataset</span><span class="p">(</span><span class="n">fs</span><span class="p">,</span><span class="w"> </span><span class="n">root_path</span><span class="p">));</span> |
| <span class="linenos">337</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">format_name</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="s">"parquet"</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">338</span><span class="w"> </span><span class="n">format</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">ParquetFileFormat</span><span class="o">></span><span class="p">();</span> |
| <span class="linenos">339</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">base_path</span><span class="p">,</span><span class="w"> </span><span class="n">CreateExampleParquetDataset</span><span class="p">(</span><span class="n">fs</span><span class="p">,</span><span class="w"> </span><span class="n">root_path</span><span class="p">));</span> |
| <span class="linenos">340</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">format_name</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="s">"parquet_hive"</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">341</span><span class="w"> </span><span class="n">format</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">make_shared</span><span class="o"><</span><span class="n">ds</span><span class="o">::</span><span class="n">ParquetFileFormat</span><span class="o">></span><span class="p">();</span> |
| <span class="linenos">342</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">base_path</span><span class="p">,</span> |
| <span class="linenos">343</span><span class="w"> </span><span class="n">CreateExampleParquetHivePartitionedDataset</span><span class="p">(</span><span class="n">fs</span><span class="p">,</span><span class="w"> </span><span class="n">root_path</span><span class="p">));</span> |
| <span class="linenos">344</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">345</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cerr</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"Unknown format: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">format_name</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> |
| <span class="linenos">346</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cerr</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"Supported formats: feather, parquet, parquet_hive"</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> |
| <span class="linenos">347</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">Status</span><span class="o">::</span><span class="n">ExecutionError</span><span class="p">(</span><span class="s">"Dataset creating failed."</span><span class="p">);</span> |
| <span class="linenos">348</span><span class="w"> </span><span class="p">}</span> |
| <span class="linenos">349</span> |
| <span class="linenos">350</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Table</span><span class="o">></span><span class="w"> </span><span class="n">table</span><span class="p">;</span> |
| <span class="linenos">351</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">mode</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="s">"no_filter"</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">352</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">table</span><span class="p">,</span><span class="w"> </span><span class="n">ScanWholeDataset</span><span class="p">(</span><span class="n">fs</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="n">base_path</span><span class="p">));</span> |
| <span class="linenos">353</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">mode</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="s">"filter"</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">354</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">table</span><span class="p">,</span><span class="w"> </span><span class="n">FilterAndSelectDataset</span><span class="p">(</span><span class="n">fs</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="n">base_path</span><span class="p">));</span> |
| <span class="linenos">355</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">mode</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="s">"project"</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">356</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">table</span><span class="p">,</span><span class="w"> </span><span class="n">ProjectDataset</span><span class="p">(</span><span class="n">fs</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="n">base_path</span><span class="p">));</span> |
| <span class="linenos">357</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">mode</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="s">"select_project"</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">358</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">table</span><span class="p">,</span><span class="w"> </span><span class="n">SelectAndProjectDataset</span><span class="p">(</span><span class="n">fs</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="n">base_path</span><span class="p">));</span> |
| <span class="linenos">359</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">mode</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="s">"partitioned"</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">360</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">table</span><span class="p">,</span><span class="w"> </span><span class="n">ScanPartitionedDataset</span><span class="p">(</span><span class="n">fs</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="n">base_path</span><span class="p">));</span> |
| <span class="linenos">361</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">mode</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="s">"filter_partitioned"</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">362</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">table</span><span class="p">,</span><span class="w"> </span><span class="n">FilterPartitionedDataset</span><span class="p">(</span><span class="n">fs</span><span class="p">,</span><span class="w"> </span><span class="n">format</span><span class="p">,</span><span class="w"> </span><span class="n">base_path</span><span class="p">));</span> |
| <span class="linenos">363</span><span class="w"> </span><span class="p">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">364</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cerr</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"Unknown mode: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">mode</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> |
| <span class="linenos">365</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cerr</span> |
| <span class="linenos">366</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"Supported modes: no_filter, filter, project, select_project, partitioned"</span> |
| <span class="linenos">367</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> |
| <span class="linenos">368</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">Status</span><span class="o">::</span><span class="n">ExecutionError</span><span class="p">(</span><span class="s">"Dataset reading failed."</span><span class="p">);</span> |
| <span class="linenos">369</span><span class="w"> </span><span class="p">}</span> |
| <span class="linenos">370</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"Read "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">table</span><span class="o">-></span><span class="n">num_rows</span><span class="p">()</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">" rows"</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> |
| <span class="linenos">371</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">table</span><span class="o">-></span><span class="n">ToString</span><span class="p">()</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> |
| <span class="linenos">372</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">Status</span><span class="o">::</span><span class="n">OK</span><span class="p">();</span> |
| <span class="linenos">373</span><span class="p">}</span> |
| <span class="linenos">374</span> |
| <span class="linenos">375</span><span class="kt">int</span><span class="w"> </span><span class="n">main</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">argc</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="o">**</span><span class="w"> </span><span class="n">argv</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">376</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">argc</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="mi">3</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">377</span><span class="w"> </span><span class="c1">// Fake success for CI purposes.</span> |
| <span class="linenos">378</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">EXIT_SUCCESS</span><span class="p">;</span> |
| <span class="linenos">379</span><span class="w"> </span><span class="p">}</span> |
| <span class="linenos">380</span> |
| <span class="linenos">381</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="w"> </span><span class="n">uri</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">];</span> |
| <span class="linenos">382</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="w"> </span><span class="n">format_name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">argv</span><span class="p">[</span><span class="mi">2</span><span class="p">];</span> |
| <span class="linenos">383</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="w"> </span><span class="n">mode</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">argc</span><span class="w"> </span><span class="o">></span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">?</span><span class="w"> </span><span class="n">argv</span><span class="p">[</span><span class="mi">3</span><span class="p">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="s">"no_filter"</span><span class="p">;</span> |
| <span class="linenos">384</span> |
| <span class="linenos">385</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">status</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RunDatasetDocumentation</span><span class="p">(</span><span class="n">format_name</span><span class="p">,</span><span class="w"> </span><span class="n">uri</span><span class="p">,</span><span class="w"> </span><span class="n">mode</span><span class="p">);</span> |
| <span class="linenos">386</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">status</span><span class="p">.</span><span class="n">ok</span><span class="p">())</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">387</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cerr</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">status</span><span class="p">.</span><span class="n">ToString</span><span class="p">()</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span> |
| <span class="linenos">388</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">EXIT_FAILURE</span><span class="p">;</span> |
| <span class="linenos">389</span><span class="w"> </span><span class="p">}</span> |
| <span class="linenos">390</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">EXIT_SUCCESS</span><span class="p">;</span> |
| <span class="linenos">391</span><span class="p">}</span> |
| </pre></div> |
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