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| <section id="reading-and-writing-csv-files"> |
| <h1>Reading and Writing CSV files<a class="headerlink" href="#reading-and-writing-csv-files" title="Permalink to this heading">#</a></h1> |
| <p>Arrow provides a fast CSV reader allowing ingestion of external data |
| to create Arrow Tables or a stream of Arrow RecordBatches.</p> |
| <div class="admonition seealso"> |
| <p class="admonition-title">See also</p> |
| <p><a class="reference internal" href="api/formats.html#cpp-api-csv"><span class="std std-ref">CSV reader/writer API reference</span></a>.</p> |
| </div> |
| <section id="reading-csv-files"> |
| <h2>Reading CSV files<a class="headerlink" href="#reading-csv-files" title="Permalink to this heading">#</a></h2> |
| <p>Data in a CSV file can either be read in as a single Arrow Table using |
| <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv11TableReaderE" title="arrow::csv::TableReader"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">TableReader</span></code></a> or streamed as RecordBatches using |
| <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv15StreamingReaderE" title="arrow::csv::StreamingReader"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">StreamingReader</span></code></a>. See <a class="reference internal" href="#cpp-csv-tradeoffs"><span class="std std-ref">Tradeoffs</span></a> for a |
| discussion of the tradeoffs between the two methods.</p> |
| <p>Both these readers require an <a class="reference internal" href="api/io.html#_CPPv4N5arrow2io11InputStreamE" title="arrow::io::InputStream"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::io::InputStream</span></code></a> instance |
| representing the input file. Their behavior can be customized using a |
| combination of <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv11ReadOptionsE" title="arrow::csv::ReadOptions"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">ReadOptions</span></code></a>, |
| <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv12ParseOptionsE" title="arrow::csv::ParseOptions"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">ParseOptions</span></code></a>, and <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv14ConvertOptionsE" title="arrow::csv::ConvertOptions"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">ConvertOptions</span></code></a>.</p> |
| <section id="tablereader"> |
| <h3>TableReader<a class="headerlink" href="#tablereader" title="Permalink to this heading">#</a></h3> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span><span class="w"> </span><span class="cpf">"arrow/csv/api.h"</span> |
| |
| <span class="p">{</span> |
| <span class="w"> </span><span class="c1">// ...</span> |
| <span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">io</span><span class="o">::</span><span class="n">IOContext</span><span class="w"> </span><span class="n">io_context</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">io</span><span class="o">::</span><span class="n">default_io_context</span><span class="p">();</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">io</span><span class="o">::</span><span class="n">InputStream</span><span class="o">></span><span class="w"> </span><span class="n">input</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">...;</span> |
| |
| <span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">read_options</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">csv</span><span class="o">::</span><span class="n">ReadOptions</span><span class="o">::</span><span class="n">Defaults</span><span class="p">();</span> |
| <span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">parse_options</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">csv</span><span class="o">::</span><span class="n">ParseOptions</span><span class="o">::</span><span class="n">Defaults</span><span class="p">();</span> |
| <span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">convert_options</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">csv</span><span class="o">::</span><span class="n">ConvertOptions</span><span class="o">::</span><span class="n">Defaults</span><span class="p">();</span> |
| |
| <span class="w"> </span><span class="c1">// Instantiate TableReader from input stream and options</span> |
| <span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">maybe_reader</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">csv</span><span class="o">::</span><span class="n">TableReader</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span><span class="n">io_context</span><span class="p">,</span> |
| <span class="w"> </span><span class="n">input</span><span class="p">,</span> |
| <span class="w"> </span><span class="n">read_options</span><span class="p">,</span> |
| <span class="w"> </span><span class="n">parse_options</span><span class="p">,</span> |
| <span class="w"> </span><span class="n">convert_options</span><span class="p">);</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">maybe_reader</span><span class="p">.</span><span class="n">ok</span><span class="p">())</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="c1">// Handle TableReader instantiation error...</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">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">csv</span><span class="o">::</span><span class="n">TableReader</span><span class="o">></span><span class="w"> </span><span class="n">reader</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">*</span><span class="n">maybe_reader</span><span class="p">;</span> |
| |
| <span class="w"> </span><span class="c1">// Read table from CSV file</span> |
| <span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">maybe_table</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">reader</span><span class="o">-></span><span class="n">Read</span><span class="p">();</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">maybe_table</span><span class="p">.</span><span class="n">ok</span><span class="p">())</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="c1">// Handle CSV read error</span> |
| <span class="w"> </span><span class="c1">// (for example a CSV syntax error or failed type conversion)</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">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="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">*</span><span class="n">maybe_table</span><span class="p">;</span> |
| <span class="p">}</span> |
| </pre></div> |
| </div> |
| </section> |
| <section id="streamingreader"> |
| <h3>StreamingReader<a class="headerlink" href="#streamingreader" title="Permalink to this heading">#</a></h3> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span><span class="w"> </span><span class="cpf">"arrow/csv/api.h"</span> |
| |
| <span class="p">{</span> |
| <span class="w"> </span><span class="c1">// ...</span> |
| <span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">io</span><span class="o">::</span><span class="n">IOContext</span><span class="w"> </span><span class="n">io_context</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">io</span><span class="o">::</span><span class="n">default_io_context</span><span class="p">();</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">io</span><span class="o">::</span><span class="n">InputStream</span><span class="o">></span><span class="w"> </span><span class="n">input</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">...;</span> |
| |
| <span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">read_options</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">csv</span><span class="o">::</span><span class="n">ReadOptions</span><span class="o">::</span><span class="n">Defaults</span><span class="p">();</span> |
| <span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">parse_options</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">csv</span><span class="o">::</span><span class="n">ParseOptions</span><span class="o">::</span><span class="n">Defaults</span><span class="p">();</span> |
| <span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">convert_options</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">csv</span><span class="o">::</span><span class="n">ConvertOptions</span><span class="o">::</span><span class="n">Defaults</span><span class="p">();</span> |
| |
| <span class="w"> </span><span class="c1">// Instantiate StreamingReader from input stream and options</span> |
| <span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">maybe_reader</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">csv</span><span class="o">::</span><span class="n">StreamingReader</span><span class="o">::</span><span class="n">Make</span><span class="p">(</span><span class="n">io_context</span><span class="p">,</span> |
| <span class="w"> </span><span class="n">input</span><span class="p">,</span> |
| <span class="w"> </span><span class="n">read_options</span><span class="p">,</span> |
| <span class="w"> </span><span class="n">parse_options</span><span class="p">,</span> |
| <span class="w"> </span><span class="n">convert_options</span><span class="p">);</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">maybe_reader</span><span class="p">.</span><span class="n">ok</span><span class="p">())</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="c1">// Handle StreamingReader instantiation error...</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">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">csv</span><span class="o">::</span><span class="n">StreamingReader</span><span class="o">></span><span class="w"> </span><span class="n">reader</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">*</span><span class="n">maybe_reader</span><span class="p">;</span> |
| |
| <span class="w"> </span><span class="c1">// Set aside a RecordBatch pointer for re-use while streaming</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">RecordBatch</span><span class="o">></span><span class="w"> </span><span class="n">batch</span><span class="p">;</span> |
| |
| <span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p">(</span><span class="nb">true</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="c1">// Attempt to read the first RecordBatch</span> |
| <span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">Status</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">reader</span><span class="o">-></span><span class="n">ReadNext</span><span class="p">(</span><span class="o">&</span><span class="n">batch</span><span class="p">);</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="w"> </span><span class="c1">// Handle read error</span> |
| <span class="w"> </span><span class="p">}</span> |
| |
| <span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">batch</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="nb">NULL</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="c1">// Handle end of file</span> |
| <span class="w"> </span><span class="k">break</span><span class="p">;</span> |
| <span class="w"> </span><span class="p">}</span> |
| |
| <span class="w"> </span><span class="c1">// Do something with the batch</span> |
| <span class="w"> </span><span class="p">}</span> |
| <span class="p">}</span> |
| </pre></div> |
| </div> |
| </section> |
| <section id="tradeoffs"> |
| <span id="cpp-csv-tradeoffs"></span><h3>Tradeoffs<a class="headerlink" href="#tradeoffs" title="Permalink to this heading">#</a></h3> |
| <p>The choice between using <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv11TableReaderE" title="arrow::csv::TableReader"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">TableReader</span></code></a> or |
| <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv15StreamingReaderE" title="arrow::csv::StreamingReader"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">StreamingReader</span></code></a> will ultimately depend on the use case |
| but there are a few tradeoffs to be aware of:</p> |
| <ol class="arabic simple"> |
| <li><p><strong>Memory usage:</strong> <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv11TableReaderE" title="arrow::csv::TableReader"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">TableReader</span></code></a> loads all of the data |
| into memory at once and, depending on the amount of data, may require |
| considerably more memory than <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv15StreamingReaderE" title="arrow::csv::StreamingReader"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">StreamingReader</span></code></a> which |
| only loads one <a class="reference internal" href="api/table.html#_CPPv4N5arrow11RecordBatchE" title="arrow::RecordBatch"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">RecordBatch</span></code></a> at a time. This is likely to be |
| the most significant tradeoff for users.</p></li> |
| <li><p><strong>Speed:</strong> When reading the entire contents of a CSV, |
| <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv11TableReaderE" title="arrow::csv::TableReader"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">TableReader</span></code></a> will tend to be faster than |
| <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv15StreamingReaderE" title="arrow::csv::StreamingReader"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">StreamingReader</span></code></a> because it makes better use of |
| available cores. See <a class="reference internal" href="#cpp-csv-performance"><span class="std std-ref">Performance</span></a> for more |
| details.</p></li> |
| <li><p><strong>Flexibility:</strong> <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv15StreamingReaderE" title="arrow::csv::StreamingReader"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">StreamingReader</span></code></a> might be considered |
| less flexible than <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv11TableReaderE" title="arrow::csv::TableReader"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">TableReader</span></code></a> because it performs type |
| inference only on the first block that’s read in, after which point the types |
| are frozen and any data in subsequent blocks that cannot be converted to |
| those types will cause an error. Note that this can be remedied either by |
| setting <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv11ReadOptions10block_sizeE" title="arrow::csv::ReadOptions::block_size"><code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">ReadOptions::block_size</span></code></a> to a large enough value or by using |
| <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv14ConvertOptions12column_typesE" title="arrow::csv::ConvertOptions::column_types"><code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">ConvertOptions::column_types</span></code></a> to set the desired data types |
| explicitly.</p></li> |
| </ol> |
| </section> |
| </section> |
| <section id="writing-csv-files"> |
| <h2>Writing CSV files<a class="headerlink" href="#writing-csv-files" title="Permalink to this heading">#</a></h2> |
| <p>A CSV file is written to a <a class="reference internal" href="api/io.html#_CPPv4N5arrow2io12OutputStreamE" title="arrow::io::OutputStream"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">OutputStream</span></code></a>.</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><arrow/csv/api.h></span> |
| <span class="p">{</span> |
| <span class="w"> </span><span class="c1">// Oneshot write</span> |
| <span class="w"> </span><span class="c1">// ...</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">io</span><span class="o">::</span><span class="n">OutputStream</span><span class="o">></span><span class="w"> </span><span class="n">output</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">...;</span> |
| <span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">write_options</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">csv</span><span class="o">::</span><span class="n">WriteOptions</span><span class="o">::</span><span class="n">Defaults</span><span class="p">();</span> |
| <span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">WriteCSV</span><span class="p">(</span><span class="n">table</span><span class="p">,</span><span class="w"> </span><span class="n">write_options</span><span class="p">,</span><span class="w"> </span><span class="n">output</span><span class="p">.</span><span class="n">get</span><span class="p">()).</span><span class="n">ok</span><span class="p">())</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="c1">// Handle writer error...</span> |
| <span class="w"> </span><span class="p">}</span> |
| <span class="p">}</span> |
| <span class="p">{</span> |
| <span class="w"> </span><span class="c1">// Write incrementally</span> |
| <span class="w"> </span><span class="c1">// ...</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">io</span><span class="o">::</span><span class="n">OutputStream</span><span class="o">></span><span class="w"> </span><span class="n">output</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">...;</span> |
| <span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">write_options</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">csv</span><span class="o">::</span><span class="n">WriteOptions</span><span class="o">::</span><span class="n">Defaults</span><span class="p">();</span> |
| <span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">maybe_writer</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">csv</span><span class="o">::</span><span class="n">MakeCSVWriter</span><span class="p">(</span><span class="n">output</span><span class="p">,</span><span class="w"> </span><span class="n">schema</span><span class="p">,</span><span class="w"> </span><span class="n">write_options</span><span class="p">);</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">maybe_writer</span><span class="p">.</span><span class="n">ok</span><span class="p">())</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="c1">// Handle writer instantiation error...</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">shared_ptr</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">ipc</span><span class="o">::</span><span class="n">RecordBatchWriter</span><span class="o">></span><span class="w"> </span><span class="n">writer</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">*</span><span class="n">maybe_writer</span><span class="p">;</span> |
| |
| <span class="w"> </span><span class="c1">// Write batches...</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">writer</span><span class="o">-></span><span class="n">WriteRecordBatch</span><span class="p">(</span><span class="o">*</span><span class="n">batch</span><span class="p">).</span><span class="n">ok</span><span class="p">())</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="c1">// Handle write error...</span> |
| <span class="w"> </span><span class="p">}</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">writer</span><span class="o">-></span><span class="n">Close</span><span class="p">().</span><span class="n">ok</span><span class="p">())</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="c1">// Handle close error...</span> |
| <span class="w"> </span><span class="p">}</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">output</span><span class="o">-></span><span class="n">Close</span><span class="p">().</span><span class="n">ok</span><span class="p">())</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="c1">// Handle file close error...</span> |
| <span class="w"> </span><span class="p">}</span> |
| <span class="p">}</span> |
| </pre></div> |
| </div> |
| <div class="admonition note"> |
| <p class="admonition-title">Note</p> |
| <p>The writer does not yet support all Arrow types.</p> |
| </div> |
| </section> |
| <section id="column-names"> |
| <h2>Column names<a class="headerlink" href="#column-names" title="Permalink to this heading">#</a></h2> |
| <p>There are three possible ways to infer column names from the CSV file:</p> |
| <ul class="simple"> |
| <li><p>By default, the column names are read from the first row in the CSV file</p></li> |
| <li><p>If <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv11ReadOptions12column_namesE" title="arrow::csv::ReadOptions::column_names"><code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">ReadOptions::column_names</span></code></a> is set, it forces the column |
| names in the table to these values (the first row in the CSV file is |
| read as data)</p></li> |
| <li><p>If <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv11ReadOptions25autogenerate_column_namesE" title="arrow::csv::ReadOptions::autogenerate_column_names"><code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">ReadOptions::autogenerate_column_names</span></code></a> is true, column names |
| will be autogenerated with the pattern “f0”, “f1”… (the first row in the |
| CSV file is read as data)</p></li> |
| </ul> |
| </section> |
| <section id="column-selection"> |
| <h2>Column selection<a class="headerlink" href="#column-selection" title="Permalink to this heading">#</a></h2> |
| <p>By default, Arrow reads all columns in the CSV file. You can narrow the |
| selection of columns with the <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv14ConvertOptions15include_columnsE" title="arrow::csv::ConvertOptions::include_columns"><code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">ConvertOptions::include_columns</span></code></a> |
| option. If some columns in <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv14ConvertOptions15include_columnsE" title="arrow::csv::ConvertOptions::include_columns"><code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">ConvertOptions::include_columns</span></code></a> |
| are missing from the CSV file, an error will be emitted unless |
| <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv14ConvertOptions23include_missing_columnsE" title="arrow::csv::ConvertOptions::include_missing_columns"><code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">ConvertOptions::include_missing_columns</span></code></a> is true, in which case |
| the missing columns are assumed to contain all-null values.</p> |
| <section id="interaction-with-column-names"> |
| <h3>Interaction with column names<a class="headerlink" href="#interaction-with-column-names" title="Permalink to this heading">#</a></h3> |
| <p>If both <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv11ReadOptions12column_namesE" title="arrow::csv::ReadOptions::column_names"><code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">ReadOptions::column_names</span></code></a> and |
| <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv14ConvertOptions15include_columnsE" title="arrow::csv::ConvertOptions::include_columns"><code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">ConvertOptions::include_columns</span></code></a> are specified, |
| the <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv11ReadOptions12column_namesE" title="arrow::csv::ReadOptions::column_names"><code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">ReadOptions::column_names</span></code></a> are assumed to map to CSV columns, |
| and <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv14ConvertOptions15include_columnsE" title="arrow::csv::ConvertOptions::include_columns"><code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">ConvertOptions::include_columns</span></code></a> is a subset of those column |
| names that will part of the Arrow Table.</p> |
| </section> |
| </section> |
| <section id="data-types"> |
| <h2>Data types<a class="headerlink" href="#data-types" title="Permalink to this heading">#</a></h2> |
| <p>By default, the CSV reader infers the most appropriate data type for each |
| column. Type inference considers the following data types, in order:</p> |
| <ul class="simple"> |
| <li><p>Null</p></li> |
| <li><p>Int64</p></li> |
| <li><p>Boolean</p></li> |
| <li><p>Date32</p></li> |
| <li><p>Time32 (with seconds unit)</p></li> |
| <li><p>Timestamp (with seconds unit)</p></li> |
| <li><p>Timestamp (with nanoseconds unit)</p></li> |
| <li><p>Float64</p></li> |
| <li><p>Dictionary<String> (if <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv14ConvertOptions16auto_dict_encodeE" title="arrow::csv::ConvertOptions::auto_dict_encode"><code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">ConvertOptions::auto_dict_encode</span></code></a> is true)</p></li> |
| <li><p>Dictionary<Binary> (if <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv14ConvertOptions16auto_dict_encodeE" title="arrow::csv::ConvertOptions::auto_dict_encode"><code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">ConvertOptions::auto_dict_encode</span></code></a> is true)</p></li> |
| <li><p>String</p></li> |
| <li><p>Binary</p></li> |
| </ul> |
| <p>It is possible to override type inference for select columns by setting |
| the <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv14ConvertOptions12column_typesE" title="arrow::csv::ConvertOptions::column_types"><code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">ConvertOptions::column_types</span></code></a> option. Explicit data types |
| can be chosen from the following list:</p> |
| <ul class="simple"> |
| <li><p>Null</p></li> |
| <li><p>All Integer types</p></li> |
| <li><p>Float32 and Float64</p></li> |
| <li><p>Decimal128</p></li> |
| <li><p>Boolean</p></li> |
| <li><p>Date32 and Date64</p></li> |
| <li><p>Time32 and Time64</p></li> |
| <li><p>Timestamp</p></li> |
| <li><p>Binary and Large Binary</p></li> |
| <li><p>String and Large String (with optional UTF8 input validation)</p></li> |
| <li><p>Fixed-Size Binary</p></li> |
| <li><p>Dictionary with index type Int32 and value type one of the following: |
| Binary, String, LargeBinary, LargeString, Int32, UInt32, Int64, UInt64, |
| Float32, Float64, Decimal128</p></li> |
| </ul> |
| <p>Other data types do not support conversion from CSV values and will error out.</p> |
| <section id="dictionary-inference"> |
| <h3>Dictionary inference<a class="headerlink" href="#dictionary-inference" title="Permalink to this heading">#</a></h3> |
| <p>If type inference is enabled and <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv14ConvertOptions16auto_dict_encodeE" title="arrow::csv::ConvertOptions::auto_dict_encode"><code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">ConvertOptions::auto_dict_encode</span></code></a> |
| is true, the CSV reader first tries to convert string-like columns to a |
| dictionary-encoded string-like array. It switches to a plain string-like |
| array when the threshold in <code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">ConvertOptions::auto_dict_max_cardinality</span></code> |
| is reached.</p> |
| </section> |
| <section id="timestamp-inference-parsing"> |
| <h3>Timestamp inference/parsing<a class="headerlink" href="#timestamp-inference-parsing" title="Permalink to this heading">#</a></h3> |
| <p>If type inference is enabled, the CSV reader first tries to interpret |
| string-like columns as timestamps. If all rows have some zone offset |
| (e.g. <code class="docutils literal notranslate"><span class="pre">Z</span></code> or <code class="docutils literal notranslate"><span class="pre">+0100</span></code>), even if the offsets are inconsistent, then the |
| inferred type will be UTC timestamp. If no rows have a zone offset, then the |
| inferred type will be timestamp without timezone. A mix of rows with/without |
| offsets will result in a string column.</p> |
| <p>If the type is explicitly specified as a timestamp with/without timezone, then |
| the reader will error on values without/with zone offsets in that column. Note |
| that this means it isn’t currently possible to have the reader parse a column |
| of timestamps without zone offsets as local times in a particular timezone; |
| instead, parse the column as timestamp without timezone, then convert the |
| values afterwards using the <code class="docutils literal notranslate"><span class="pre">assume_timezone</span></code> compute function.</p> |
| <table class="table"> |
| <thead> |
| <tr class="row-odd"><th class="head"><p>Specified Type</p></th> |
| <th class="head"><p>Input CSV</p></th> |
| <th class="head"><p>Result Type</p></th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr class="row-even"><td rowspan="4"><p>(inferred)</p></td> |
| <td><p><code class="docutils literal notranslate"><span class="pre">2021-01-01T00:00:00</span></code></p></td> |
| <td><p>timestamp[s]</p></td> |
| </tr> |
| <tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">2021-01-01T00:00:00Z</span></code></p></td> |
| <td rowspan="2"><p>timestamp[s, UTC]</p></td> |
| </tr> |
| <tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">2021-01-01T00:00:00+0100</span></code></p></td> |
| </tr> |
| <tr class="row-odd"><td><div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="mi">2021</span><span class="mo">-01-01</span><span class="n">T00</span><span class="o">:</span><span class="mo">00</span><span class="o">:</span><span class="mo">00</span> |
| <span class="mi">2021</span><span class="mo">-01-01</span><span class="n">T00</span><span class="o">:</span><span class="mo">00</span><span class="o">:</span><span class="mo">00</span><span class="n">Z</span> |
| </pre></div> |
| </div> |
| </td> |
| <td><p>string</p></td> |
| </tr> |
| <tr class="row-even"><td rowspan="4"><p>timestamp[s]</p></td> |
| <td><p><code class="docutils literal notranslate"><span class="pre">2021-01-01T00:00:00</span></code></p></td> |
| <td><p>timestamp[s]</p></td> |
| </tr> |
| <tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">2021-01-01T00:00:00Z</span></code></p></td> |
| <td rowspan="3"><p>(error)</p></td> |
| </tr> |
| <tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">2021-01-01T00:00:00+0100</span></code></p></td> |
| </tr> |
| <tr class="row-odd"><td><div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="mi">2021</span><span class="mo">-01-01</span><span class="n">T00</span><span class="o">:</span><span class="mo">00</span><span class="o">:</span><span class="mo">00</span> |
| <span class="mi">2021</span><span class="mo">-01-01</span><span class="n">T00</span><span class="o">:</span><span class="mo">00</span><span class="o">:</span><span class="mo">00</span><span class="n">Z</span> |
| </pre></div> |
| </div> |
| </td> |
| </tr> |
| <tr class="row-even"><td rowspan="4"><p>timestamp[s, UTC]</p></td> |
| <td><p><code class="docutils literal notranslate"><span class="pre">2021-01-01T00:00:00</span></code></p></td> |
| <td><p>(error)</p></td> |
| </tr> |
| <tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">2021-01-01T00:00:00Z</span></code></p></td> |
| <td rowspan="2"><p>timestamp[s, UTC]</p></td> |
| </tr> |
| <tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">2021-01-01T00:00:00+0100</span></code></p></td> |
| </tr> |
| <tr class="row-odd"><td><div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="mi">2021</span><span class="mo">-01-01</span><span class="n">T00</span><span class="o">:</span><span class="mo">00</span><span class="o">:</span><span class="mo">00</span> |
| <span class="mi">2021</span><span class="mo">-01-01</span><span class="n">T00</span><span class="o">:</span><span class="mo">00</span><span class="o">:</span><span class="mo">00</span><span class="n">Z</span> |
| </pre></div> |
| </div> |
| </td> |
| <td><p>(error)</p></td> |
| </tr> |
| <tr class="row-even"><td rowspan="4"><p>timestamp[s, |
| America/New_York]</p></td> |
| <td><p><code class="docutils literal notranslate"><span class="pre">2021-01-01T00:00:00</span></code></p></td> |
| <td><p>(error)</p></td> |
| </tr> |
| <tr class="row-odd"><td><p><code class="docutils literal notranslate"><span class="pre">2021-01-01T00:00:00Z</span></code></p></td> |
| <td rowspan="2"><p>timestamp[s, |
| America/New_York]</p></td> |
| </tr> |
| <tr class="row-even"><td><p><code class="docutils literal notranslate"><span class="pre">2021-01-01T00:00:00+0100</span></code></p></td> |
| </tr> |
| <tr class="row-odd"><td><div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="mi">2021</span><span class="mo">-01-01</span><span class="n">T00</span><span class="o">:</span><span class="mo">00</span><span class="o">:</span><span class="mo">00</span> |
| <span class="mi">2021</span><span class="mo">-01-01</span><span class="n">T00</span><span class="o">:</span><span class="mo">00</span><span class="o">:</span><span class="mo">00</span><span class="n">Z</span> |
| </pre></div> |
| </div> |
| </td> |
| <td><p>(error)</p></td> |
| </tr> |
| </tbody> |
| </table> |
| </section> |
| <section id="nulls"> |
| <h3>Nulls<a class="headerlink" href="#nulls" title="Permalink to this heading">#</a></h3> |
| <p>Null values are recognized from the spellings stored in |
| <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv14ConvertOptions11null_valuesE" title="arrow::csv::ConvertOptions::null_values"><code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">ConvertOptions::null_values</span></code></a>. The <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv14ConvertOptions8DefaultsEv" title="arrow::csv::ConvertOptions::Defaults"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">ConvertOptions::Defaults()</span></code></a> |
| factory method will initialize a number of conventional null spellings such |
| as <code class="docutils literal notranslate"><span class="pre">N/A</span></code>.</p> |
| </section> |
| <section id="character-encoding"> |
| <h3>Character encoding<a class="headerlink" href="#character-encoding" title="Permalink to this heading">#</a></h3> |
| <p>CSV files are expected to be encoded in UTF8. However, non-UTF8 data |
| is accepted for Binary columns.</p> |
| </section> |
| </section> |
| <section id="write-options"> |
| <h2>Write Options<a class="headerlink" href="#write-options" title="Permalink to this heading">#</a></h2> |
| <p>The format of written CSV files can be customized via <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv12WriteOptionsE" title="arrow::csv::WriteOptions"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">WriteOptions</span></code></a>. |
| Currently few options are available; more will be added in future releases.</p> |
| </section> |
| <section id="performance"> |
| <span id="cpp-csv-performance"></span><h2>Performance<a class="headerlink" href="#performance" title="Permalink to this heading">#</a></h2> |
| <p>By default, <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv11TableReaderE" title="arrow::csv::TableReader"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">TableReader</span></code></a> will parallelize reads in order to |
| exploit all CPU cores on your machine. You can change this setting in |
| <a class="reference internal" href="api/formats.html#_CPPv4N5arrow3csv11ReadOptions11use_threadsE" title="arrow::csv::ReadOptions::use_threads"><code class="xref cpp cpp-member docutils literal notranslate"><span class="pre">ReadOptions::use_threads</span></code></a>. A reasonable expectation is at least |
| 100 MB/s per core on a performant desktop or laptop computer (measured in |
| source CSV bytes, not target Arrow data bytes).</p> |
| </section> |
| </section> |
| |
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