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| <div class="section" id="reading-csv-files"> |
| <span id="csv"></span><h1>Reading CSV files<a class="headerlink" href="#reading-csv-files" title="Permalink to this headline">¶</a></h1> |
| <p>Arrow supports reading columnar data from CSV files. |
| The features currently offered are the following:</p> |
| <ul class="simple"> |
| <li><p>multi-threaded or single-threaded reading</p></li> |
| <li><p>automatic decompression of input files (based on the filename extension, |
| such as <code class="docutils literal notranslate"><span class="pre">my_data.csv.gz</span></code>)</p></li> |
| <li><p>fetching column names from the first row in the CSV file</p></li> |
| <li><p>column-wise type inference and conversion to one of <code class="docutils literal notranslate"><span class="pre">null</span></code>, <code class="docutils literal notranslate"><span class="pre">int64</span></code>, |
| <code class="docutils literal notranslate"><span class="pre">float64</span></code>, <code class="docutils literal notranslate"><span class="pre">date32</span></code>, <code class="docutils literal notranslate"><span class="pre">timestamp[s]</span></code>, <code class="docutils literal notranslate"><span class="pre">string</span></code> or <code class="docutils literal notranslate"><span class="pre">binary</span></code> data</p></li> |
| <li><p>opportunistic dictionary encoding of <code class="docutils literal notranslate"><span class="pre">string</span></code> and <code class="docutils literal notranslate"><span class="pre">binary</span></code> columns |
| (disabled by default)</p></li> |
| <li><p>detecting various spellings of null values such as <code class="docutils literal notranslate"><span class="pre">NaN</span></code> or <code class="docutils literal notranslate"><span class="pre">#N/A</span></code></p></li> |
| </ul> |
| <div class="section" id="usage"> |
| <h2>Usage<a class="headerlink" href="#usage" title="Permalink to this headline">¶</a></h2> |
| <p>CSV reading functionality is available through the <code class="xref py py-mod docutils literal notranslate"><span class="pre">pyarrow.csv</span></code> module. |
| In many cases, you will simply call the <a class="reference internal" href="generated/pyarrow.csv.read_csv.html#pyarrow.csv.read_csv" title="pyarrow.csv.read_csv"><code class="xref py py-func docutils literal notranslate"><span class="pre">read_csv()</span></code></a> function |
| with the file path you want to read from:</p> |
| <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">pyarrow</span> <span class="k">import</span> <span class="n">csv</span> |
| <span class="gp">>>> </span><span class="n">fn</span> <span class="o">=</span> <span class="s1">'tips.csv.gz'</span> |
| <span class="gp">>>> </span><span class="n">table</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">read_csv</span><span class="p">(</span><span class="n">fn</span><span class="p">)</span> |
| <span class="gp">>>> </span><span class="n">table</span> |
| <span class="go">pyarrow.Table</span> |
| <span class="go">total_bill: double</span> |
| <span class="go">tip: double</span> |
| <span class="go">sex: string</span> |
| <span class="go">smoker: string</span> |
| <span class="go">day: string</span> |
| <span class="go">time: string</span> |
| <span class="go">size: int64</span> |
| <span class="gp">>>> </span><span class="nb">len</span><span class="p">(</span><span class="n">table</span><span class="p">)</span> |
| <span class="go">244</span> |
| <span class="gp">>>> </span><span class="n">df</span> <span class="o">=</span> <span class="n">table</span><span class="o">.</span><span class="n">to_pandas</span><span class="p">()</span> |
| <span class="gp">>>> </span><span class="n">df</span><span class="o">.</span><span class="n">head</span><span class="p">()</span> |
| <span class="go"> total_bill tip sex smoker day time size</span> |
| <span class="go">0 16.99 1.01 Female No Sun Dinner 2</span> |
| <span class="go">1 10.34 1.66 Male No Sun Dinner 3</span> |
| <span class="go">2 21.01 3.50 Male No Sun Dinner 3</span> |
| <span class="go">3 23.68 3.31 Male No Sun Dinner 2</span> |
| <span class="go">4 24.59 3.61 Female No Sun Dinner 4</span> |
| </pre></div> |
| </div> |
| </div> |
| <div class="section" id="customized-parsing"> |
| <h2>Customized parsing<a class="headerlink" href="#customized-parsing" title="Permalink to this headline">¶</a></h2> |
| <p>To alter the default parsing settings in case of reading CSV files with an |
| unusual structure, you should create a <a class="reference internal" href="generated/pyarrow.csv.ParseOptions.html#pyarrow.csv.ParseOptions" title="pyarrow.csv.ParseOptions"><code class="xref py py-class docutils literal notranslate"><span class="pre">ParseOptions</span></code></a> instance |
| and pass it to <a class="reference internal" href="generated/pyarrow.csv.read_csv.html#pyarrow.csv.read_csv" title="pyarrow.csv.read_csv"><code class="xref py py-func docutils literal notranslate"><span class="pre">read_csv()</span></code></a>.</p> |
| </div> |
| <div class="section" id="customized-conversion"> |
| <h2>Customized conversion<a class="headerlink" href="#customized-conversion" title="Permalink to this headline">¶</a></h2> |
| <p>To alter how CSV data is converted to Arrow types and data, you should create |
| a <a class="reference internal" href="generated/pyarrow.csv.ConvertOptions.html#pyarrow.csv.ConvertOptions" title="pyarrow.csv.ConvertOptions"><code class="xref py py-class docutils literal notranslate"><span class="pre">ConvertOptions</span></code></a> instance and pass it to <a class="reference internal" href="generated/pyarrow.csv.read_csv.html#pyarrow.csv.read_csv" title="pyarrow.csv.read_csv"><code class="xref py py-func docutils literal notranslate"><span class="pre">read_csv()</span></code></a>.</p> |
| </div> |
| <div class="section" id="incremental-reading"> |
| <h2>Incremental reading<a class="headerlink" href="#incremental-reading" title="Permalink to this headline">¶</a></h2> |
| <p>For memory-constrained environments, it is also possible to read a CSV file |
| one batch at a time, using <a class="reference internal" href="generated/pyarrow.csv.open_csv.html#pyarrow.csv.open_csv" title="pyarrow.csv.open_csv"><code class="xref py py-func docutils literal notranslate"><span class="pre">open_csv()</span></code></a>. It currently doesn’t support |
| parallel reading.</p> |
| </div> |
| <div class="section" id="character-encoding"> |
| <h2>Character encoding<a class="headerlink" href="#character-encoding" title="Permalink to this headline">¶</a></h2> |
| <p>By default, CSV files are expected to be encoded in UTF8. Non-UTF8 data |
| is accepted for <code class="docutils literal notranslate"><span class="pre">binary</span></code> columns. The encoding can be changed using |
| the <a class="reference internal" href="generated/pyarrow.csv.ReadOptions.html#pyarrow.csv.ReadOptions" title="pyarrow.csv.ReadOptions"><code class="xref py py-class docutils literal notranslate"><span class="pre">ReadOptions</span></code></a> class.</p> |
| </div> |
| <div class="section" id="performance"> |
| <h2>Performance<a class="headerlink" href="#performance" title="Permalink to this headline">¶</a></h2> |
| <p>Due to the structure of CSV files, one cannot expect the same levels of |
| performance as when reading dedicated binary formats like |
| <a class="reference internal" href="parquet.html#parquet"><span class="std std-ref">Parquet</span></a>. Nevertheless, Arrow strives to reduce the |
| overhead of reading CSV files. 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> |
| <p>Performance options can be controlled through the <a class="reference internal" href="generated/pyarrow.csv.ReadOptions.html#pyarrow.csv.ReadOptions" title="pyarrow.csv.ReadOptions"><code class="xref py py-class docutils literal notranslate"><span class="pre">ReadOptions</span></code></a> class. |
| Multi-threaded reading is the default for highest performance, distributing |
| the workload efficiently over all available cores.</p> |
| <div class="admonition note"> |
| <p class="admonition-title">Note</p> |
| <p>The number of concurrent threads is automatically inferred by Arrow. |
| You can inspect and change it using the <a class="reference internal" href="generated/pyarrow.cpu_count.html#pyarrow.cpu_count" title="pyarrow.cpu_count"><code class="xref py py-func docutils literal notranslate"><span class="pre">cpu_count()</span></code></a> |
| and <a class="reference internal" href="generated/pyarrow.set_cpu_count.html#pyarrow.set_cpu_count" title="pyarrow.set_cpu_count"><code class="xref py py-func docutils literal notranslate"><span class="pre">set_cpu_count()</span></code></a> functions, respectively.</p> |
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