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| <div class="section" id="reading-json-files"> |
| <span id="json"></span><h1>Reading JSON files<a class="headerlink" href="#reading-json-files" title="Permalink to this headline">¶</a></h1> |
| <p>Arrow supports reading columnar data from line-delimited JSON files. |
| In this context, a JSON file consists of multiple JSON objects, one per line, |
| representing individual data rows. For example, this file represents |
| two rows of data with four columns “a”, “b”, “c”, “d”:</p> |
| <div class="highlight-json notranslate"><div class="highlight"><pre><span></span><span class="p">{</span><span class="nt">"a"</span><span class="p">:</span> <span class="mi">1</span><span class="p">,</span> <span class="nt">"b"</span><span class="p">:</span> <span class="mf">2.0</span><span class="p">,</span> <span class="nt">"c"</span><span class="p">:</span> <span class="s2">"foo"</span><span class="p">,</span> <span class="nt">"d"</span><span class="p">:</span> <span class="kc">false</span><span class="p">}</span> |
| <span class="p">{</span><span class="nt">"a"</span><span class="p">:</span> <span class="mi">4</span><span class="p">,</span> <span class="nt">"b"</span><span class="p">:</span> <span class="mf">-5.5</span><span class="p">,</span> <span class="nt">"c"</span><span class="p">:</span> <span class="kc">null</span><span class="p">,</span> <span class="nt">"d"</span><span class="p">:</span> <span class="kc">true</span><span class="p">}</span> |
| </pre></div> |
| </div> |
| <p>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.json.gz</span></code>)</p></li> |
| <li><p>sophisticated type inference (see below)</p></li> |
| </ul> |
| <div class="admonition note"> |
| <p class="admonition-title">Note</p> |
| <p>Currently only the line-delimited JSON format is supported.</p> |
| </div> |
| <div class="section" id="usage"> |
| <h2>Usage<a class="headerlink" href="#usage" title="Permalink to this headline">¶</a></h2> |
| <p>JSON reading functionality is available through the <code class="xref py py-mod docutils literal notranslate"><span class="pre">pyarrow.json</span></code> module. |
| In many cases, you will simply call the <a class="reference internal" href="generated/pyarrow.json.read_json.html#pyarrow.json.read_json" title="pyarrow.json.read_json"><code class="xref py py-func docutils literal notranslate"><span class="pre">read_json()</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">json</span> |
| <span class="gp">>>> </span><span class="n">fn</span> <span class="o">=</span> <span class="s1">'my_data.json'</span> |
| <span class="gp">>>> </span><span class="n">table</span> <span class="o">=</span> <span class="n">json</span><span class="o">.</span><span class="n">read_json</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">a: int64</span> |
| <span class="go">b: double</span> |
| <span class="go">c: string</span> |
| <span class="go">d: bool</span> |
| <span class="gp">>>> </span><span class="n">table</span><span class="o">.</span><span class="n">to_pandas</span><span class="p">()</span> |
| <span class="go"> a b c d</span> |
| <span class="go">0 1 2.0 foo False</span> |
| <span class="go">1 4 -5.5 None True</span> |
| </pre></div> |
| </div> |
| </div> |
| <div class="section" id="automatic-type-inference"> |
| <h2>Automatic Type Inference<a class="headerlink" href="#automatic-type-inference" title="Permalink to this headline">¶</a></h2> |
| <p>Arrow <a class="reference internal" href="data.html#data-types"><span class="std std-ref">data types</span></a> are inferred from the JSON types and |
| values of each column:</p> |
| <ul class="simple"> |
| <li><p>JSON null values convert to the <code class="docutils literal notranslate"><span class="pre">null</span></code> type, but can fall back to any |
| other type.</p></li> |
| <li><p>JSON booleans convert to <code class="docutils literal notranslate"><span class="pre">bool_</span></code>.</p></li> |
| <li><p>JSON numbers convert to <code class="docutils literal notranslate"><span class="pre">int64</span></code>, falling back to <code class="docutils literal notranslate"><span class="pre">float64</span></code> if a |
| non-integer is encountered.</p></li> |
| <li><p>JSON strings of the kind “YYYY-MM-DD” and “YYYY-MM-DD hh:mm:ss” convert |
| to <code class="docutils literal notranslate"><span class="pre">timestamp[s]</span></code>, falling back to <code class="docutils literal notranslate"><span class="pre">utf8</span></code> if a conversion error occurs.</p></li> |
| <li><p>JSON arrays convert to a <code class="docutils literal notranslate"><span class="pre">list</span></code> type, and inference proceeds recursively |
| on the JSON arrays’ values.</p></li> |
| <li><p>Nested JSON objects convert to a <code class="docutils literal notranslate"><span class="pre">struct</span></code> type, and inference proceeds |
| recursively on the JSON objects’ values.</p></li> |
| </ul> |
| <p>Thus, reading this JSON file:</p> |
| <div class="highlight-json notranslate"><div class="highlight"><pre><span></span><span class="p">{</span><span class="nt">"a"</span><span class="p">:</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">],</span> <span class="nt">"b"</span><span class="p">:</span> <span class="p">{</span><span class="nt">"c"</span><span class="p">:</span> <span class="kc">true</span><span class="p">,</span> <span class="nt">"d"</span><span class="p">:</span> <span class="s2">"1991-02-03"</span><span class="p">}}</span> |
| <span class="p">{</span><span class="nt">"a"</span><span class="p">:</span> <span class="p">[</span><span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">],</span> <span class="nt">"b"</span><span class="p">:</span> <span class="p">{</span><span class="nt">"c"</span><span class="p">:</span> <span class="kc">false</span><span class="p">,</span> <span class="nt">"d"</span><span class="p">:</span> <span class="s2">"2019-04-01"</span><span class="p">}}</span> |
| </pre></div> |
| </div> |
| <p>returns the following data:</p> |
| <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">table</span> <span class="o">=</span> <span class="n">json</span><span class="o">.</span><span class="n">read_json</span><span class="p">(</span><span class="s2">"my_data.json"</span><span class="p">)</span> |
| <span class="gp">>>> </span><span class="n">table</span> |
| <span class="go">pyarrow.Table</span> |
| <span class="go">a: list<item: int64></span> |
| <span class="go"> child 0, item: int64</span> |
| <span class="go">b: struct<c: bool, d: timestamp[s]></span> |
| <span class="go"> child 0, c: bool</span> |
| <span class="go"> child 1, d: timestamp[s]</span> |
| <span class="gp">>>> </span><span class="n">table</span><span class="o">.</span><span class="n">to_pandas</span><span class="p">()</span> |
| <span class="go"> a b</span> |
| <span class="go">0 [1, 2] {'c': True, 'd': 1991-02-03 00:00:00}</span> |
| <span class="go">1 [3, 4, 5] {'c': False, 'd': 2019-04-01 00:00:00}</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 JSON files with an |
| unusual structure, you should create a <a class="reference internal" href="generated/pyarrow.json.ParseOptions.html#pyarrow.json.ParseOptions" title="pyarrow.json.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.json.read_json.html#pyarrow.json.read_json" title="pyarrow.json.read_json"><code class="xref py py-func docutils literal notranslate"><span class="pre">read_json()</span></code></a>. For example, you can pass an explicit |
| <a class="reference internal" href="data.html#data-schema"><span class="std std-ref">schema</span></a> in order to bypass automatic type inference.</p> |
| <p>Similarly, you can choose performance settings by passing a |
| <a class="reference internal" href="generated/pyarrow.json.ReadOptions.html#pyarrow.json.ReadOptions" title="pyarrow.json.ReadOptions"><code class="xref py py-class docutils literal notranslate"><span class="pre">ReadOptions</span></code></a> instance to <a class="reference internal" href="generated/pyarrow.json.read_json.html#pyarrow.json.read_json" title="pyarrow.json.read_json"><code class="xref py py-func docutils literal notranslate"><span class="pre">read_json()</span></code></a>.</p> |
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