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 </div>
 </div>


 <div id="searchbox"></div>
                 <article class="bd-article">

   <section id="tabular-data">
 <h1>Tabular Data<a class="headerlink" href="#tabular-data" title="Permalink to this heading">#</a></h1>
 <p>While arrays (aka: <a class="reference internal" href="vector.html"><span class="doc">ValueVector</span></a>) represent a one-dimensional sequence of
 homogeneous values, data often comes in the form of two-dimensional sets of
 heterogeneous data (such as database tables, CSV files…). Arrow provides
 several abstractions to handle such data conveniently and efficiently.</p>
 <section id="fields">
 <h2>Fields<a class="headerlink" href="#fields" title="Permalink to this heading">#</a></h2>
 <p>Fields are used to denote the particular columns of tabular data.
 A field, i.e. an instance of <a class="reference external" href="https://arrow.apache.org/docs/java/reference/org/apache/arrow/vector/types/pojo/Field.html">Field</a>, holds together a field name, a data
 type, and some optional key-value metadata.</p>
 <div class="highlight-Java notranslate"><div class="highlight"><pre><span></span><span class="c1">// Create a column &quot;document&quot; of string type with metadata</span>
 <span class="kn">import</span><span class="w"> </span><span class="nn">org.apache.arrow.vector.types.pojo.ArrowType</span><span class="p">;</span>
 <span class="kn">import</span><span class="w"> </span><span class="nn">org.apache.arrow.vector.types.pojo.Field</span><span class="p">;</span>
 <span class="kn">import</span><span class="w"> </span><span class="nn">org.apache.arrow.vector.types.pojo.FieldType</span><span class="p">;</span>

 <span class="n">Map</span><span class="o">&lt;</span><span class="n">String</span><span class="p">,</span><span class="w"> </span><span class="n">String</span><span class="o">&gt;</span><span class="w"> </span><span class="n">metadata</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">HashMap</span><span class="o">&lt;&gt;</span><span class="p">();</span>
 <span class="n">metadata</span><span class="p">.</span><span class="na">put</span><span class="p">(</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Id card&quot;</span><span class="p">);</span>
 <span class="n">metadata</span><span class="p">.</span><span class="na">put</span><span class="p">(</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Passport&quot;</span><span class="p">);</span>
 <span class="n">metadata</span><span class="p">.</span><span class="na">put</span><span class="p">(</span><span class="s">&quot;C&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;Visa&quot;</span><span class="p">);</span>
 <span class="n">Field</span><span class="w"> </span><span class="n">document</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Field</span><span class="p">(</span><span class="s">&quot;document&quot;</span><span class="p">,</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">FieldType</span><span class="p">(</span><span class="kc">true</span><span class="p">,</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">ArrowType</span><span class="p">.</span><span class="na">Utf8</span><span class="p">(),</span><span class="w"> </span><span class="cm">/*dictionary*/</span><span class="w"> </span><span class="kc">null</span><span class="p">,</span><span class="w"> </span><span class="n">metadata</span><span class="p">),</span><span class="w"> </span><span class="cm">/*children*/</span><span class="w"> </span><span class="kc">null</span><span class="p">);</span>
 </pre></div>
 </div>
 </section>
 <section id="schemas">
 <h2>Schemas<a class="headerlink" href="#schemas" title="Permalink to this heading">#</a></h2>
 <p>A <a class="reference external" href="https://arrow.apache.org/docs/java/reference/org/apache/arrow/vector/types/pojo/Schema.html">Schema</a> describes the overall structure consisting of any number of columns. It holds a sequence of fields together
 with some optional schema-wide metadata (in addition to per-field metadata).</p>
 <div class="highlight-Java notranslate"><div class="highlight"><pre><span></span><span class="c1">// Create a schema describing datasets with two columns:</span>
 <span class="c1">// a int32 column &quot;A&quot; and a utf8-encoded string column &quot;B&quot;</span>
 <span class="kn">import</span><span class="w"> </span><span class="nn">org.apache.arrow.vector.types.pojo.ArrowType</span><span class="p">;</span>
 <span class="kn">import</span><span class="w"> </span><span class="nn">org.apache.arrow.vector.types.pojo.Field</span><span class="p">;</span>
 <span class="kn">import</span><span class="w"> </span><span class="nn">org.apache.arrow.vector.types.pojo.FieldType</span><span class="p">;</span>
 <span class="kn">import</span><span class="w"> </span><span class="nn">org.apache.arrow.vector.types.pojo.Schema</span><span class="p">;</span>
 <span class="kn">import static</span><span class="w"> </span><span class="nn">java.util.Arrays.asList</span><span class="p">;</span>

 <span class="n">Map</span><span class="o">&lt;</span><span class="n">String</span><span class="p">,</span><span class="w"> </span><span class="n">String</span><span class="o">&gt;</span><span class="w"> </span><span class="n">metadata</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">HashMap</span><span class="o">&lt;&gt;</span><span class="p">();</span>
 <span class="n">metadata</span><span class="p">.</span><span class="na">put</span><span class="p">(</span><span class="s">&quot;K1&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;V1&quot;</span><span class="p">);</span>
 <span class="n">metadata</span><span class="p">.</span><span class="na">put</span><span class="p">(</span><span class="s">&quot;K2&quot;</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;V2&quot;</span><span class="p">);</span>
 <span class="n">Field</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Field</span><span class="p">(</span><span class="s">&quot;A&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">FieldType</span><span class="p">.</span><span class="na">nullable</span><span class="p">(</span><span class="k">new</span><span class="w"> </span><span class="n">ArrowType</span><span class="p">.</span><span class="na">Int</span><span class="p">(</span><span class="mi">32</span><span class="p">,</span><span class="w"> </span><span class="kc">true</span><span class="p">)),</span><span class="w"> </span><span class="kc">null</span><span class="p">);</span>
 <span class="n">Field</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Field</span><span class="p">(</span><span class="s">&quot;B&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">FieldType</span><span class="p">.</span><span class="na">nullable</span><span class="p">(</span><span class="k">new</span><span class="w"> </span><span class="n">ArrowType</span><span class="p">.</span><span class="na">Utf8</span><span class="p">()),</span><span class="w"> </span><span class="kc">null</span><span class="p">);</span>
 <span class="n">Schema</span><span class="w"> </span><span class="n">schema</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Schema</span><span class="p">(</span><span class="n">asList</span><span class="p">(</span><span class="n">a</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">),</span><span class="w"> </span><span class="n">metadata</span><span class="p">);</span>
 </pre></div>
 </div>
 </section>
 <section id="vectorschemaroot">
 <h2>VectorSchemaRoot<a class="headerlink" href="#vectorschemaroot" title="Permalink to this heading">#</a></h2>
 <p>A <a class="reference external" href="https://arrow.apache.org/docs/java/reference/org/apache/arrow/vector/VectorSchemaRoot.html">VectorSchemaRoot</a> is a container for batches of data. Batches flow through
 VectorSchemaRoot as part of a pipeline.</p>
 <div class="admonition note">
 <p class="admonition-title">Note</p>
 <p>VectorSchemaRoot is somewhat analogous to tables or record batches in the
 other Arrow implementations in that they all are 2D datasets, but their
 usage is different.</p>
 </div>
 <p>The recommended usage is to create a single VectorSchemaRoot based on a known
 schema and populate data over and over into that root in a stream of batches,
 rather than creating a new instance each time (see <a class="reference external" href="https://arrow.apache.org/docs/java/reference/org/apache/arrow/flight/package-summary.html">Flight</a> or
 <code class="docutils literal notranslate"><span class="pre">ArrowFileWriter</span></code> as examples). Thus at any one point, a VectorSchemaRoot may
 have data or may have no data (say it was transferred downstream or not yet
 populated).</p>
 <p>Here is an example of creating a VectorSchemaRoot:</p>
 <div class="highlight-Java notranslate"><div class="highlight"><pre><span></span><span class="n">BitVector</span><span class="w"> </span><span class="n">bitVector</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">BitVector</span><span class="p">(</span><span class="s">&quot;boolean&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">allocator</span><span class="p">);</span>
 <span class="n">VarCharVector</span><span class="w"> </span><span class="n">varCharVector</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">VarCharVector</span><span class="p">(</span><span class="s">&quot;varchar&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">allocator</span><span class="p">);</span>
 <span class="n">bitVector</span><span class="p">.</span><span class="na">allocateNew</span><span class="p">();</span>
 <span class="n">varCharVector</span><span class="p">.</span><span class="na">allocateNew</span><span class="p">();</span>
 <span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">10</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
 <span class="w">  </span><span class="n">bitVector</span><span class="p">.</span><span class="na">setSafe</span><span class="p">(</span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">%</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">?</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="mi">1</span><span class="p">);</span>
 <span class="w">  </span><span class="n">varCharVector</span><span class="p">.</span><span class="na">setSafe</span><span class="p">(</span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="p">(</span><span class="s">&quot;test&quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">i</span><span class="p">).</span><span class="na">getBytes</span><span class="p">(</span><span class="n">StandardCharsets</span><span class="p">.</span><span class="na">UTF_8</span><span class="p">));</span>
 <span class="p">}</span>
 <span class="n">bitVector</span><span class="p">.</span><span class="na">setValueCount</span><span class="p">(</span><span class="mi">10</span><span class="p">);</span>
 <span class="n">varCharVector</span><span class="p">.</span><span class="na">setValueCount</span><span class="p">(</span><span class="mi">10</span><span class="p">);</span>

 <span class="n">List</span><span class="o">&lt;</span><span class="n">Field</span><span class="o">&gt;</span><span class="w"> </span><span class="n">fields</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Arrays</span><span class="p">.</span><span class="na">asList</span><span class="p">(</span><span class="n">bitVector</span><span class="p">.</span><span class="na">getField</span><span class="p">(),</span><span class="w"> </span><span class="n">varCharVector</span><span class="p">.</span><span class="na">getField</span><span class="p">());</span>
 <span class="n">List</span><span class="o">&lt;</span><span class="n">FieldVector</span><span class="o">&gt;</span><span class="w"> </span><span class="n">vectors</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Arrays</span><span class="p">.</span><span class="na">asList</span><span class="p">(</span><span class="n">bitVector</span><span class="p">,</span><span class="w"> </span><span class="n">varCharVector</span><span class="p">);</span>
 <span class="n">VectorSchemaRoot</span><span class="w"> </span><span class="n">vectorSchemaRoot</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">VectorSchemaRoot</span><span class="p">(</span><span class="n">fields</span><span class="p">,</span><span class="w"> </span><span class="n">vectors</span><span class="p">);</span>
 </pre></div>
 </div>
 <p>Data can be loaded into/unloaded from a VectorSchemaRoot via <a class="reference external" href="https://arrow.apache.org/docs/java/reference/org/apache/arrow/vector/VectorLoader.html">VectorLoader</a>
 and <a class="reference external" href="https://arrow.apache.org/docs/java/reference/org/apache/arrow/vector/VectorUnloader.html">VectorUnloader</a>.  They handle converting between VectorSchemaRoot and
 <a class="reference external" href="https://arrow.apache.org/docs/java/reference/org/apache/arrow/vector/ipc/message/ArrowRecordBatch.html">ArrowRecordBatch</a> (a representation of a RecordBatch <a class="reference internal" href="../format/Columnar.html#format-ipc"><span class="std std-ref">IPC</span></a>
 message). For example:</p>
 <div class="highlight-Java notranslate"><div class="highlight"><pre><span></span><span class="c1">// create a VectorSchemaRoot root1 and convert its data into recordBatch</span>
 <span class="n">VectorSchemaRoot</span><span class="w"> </span><span class="n">root1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">VectorSchemaRoot</span><span class="p">(</span><span class="n">fields</span><span class="p">,</span><span class="w"> </span><span class="n">vectors</span><span class="p">);</span>
 <span class="n">VectorUnloader</span><span class="w"> </span><span class="n">unloader</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">VectorUnloader</span><span class="p">(</span><span class="n">root1</span><span class="p">);</span>
 <span class="n">ArrowRecordBatch</span><span class="w"> </span><span class="n">recordBatch</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">unloader</span><span class="p">.</span><span class="na">getRecordBatch</span><span class="p">();</span>

 <span class="c1">// create a VectorSchemaRoot root2 and load the recordBatch</span>
 <span class="n">VectorSchemaRoot</span><span class="w"> </span><span class="n">root2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">VectorSchemaRoot</span><span class="p">.</span><span class="na">create</span><span class="p">(</span><span class="n">root1</span><span class="p">.</span><span class="na">getSchema</span><span class="p">(),</span><span class="w"> </span><span class="n">allocator</span><span class="p">);</span>
 <span class="n">VectorLoader</span><span class="w"> </span><span class="n">loader</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">VectorLoader</span><span class="p">(</span><span class="n">root2</span><span class="p">);</span>
 <span class="n">loader</span><span class="p">.</span><span class="na">load</span><span class="p">(</span><span class="n">recordBatch</span><span class="p">);</span>
 </pre></div>
 </div>
 <p>A new VectorSchemaRoot can be sliced from an existing root without copying
 data:</p>
 <div class="highlight-Java notranslate"><div class="highlight"><pre><span></span><span class="c1">// 0 indicates start index (inclusive) and 5 indicated length (exclusive).</span>
 <span class="n">VectorSchemaRoot</span><span class="w"> </span><span class="n">newRoot</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">vectorSchemaRoot</span><span class="p">.</span><span class="na">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>
 </pre></div>
 </div>
 </section>
 <section id="table">
 <h2>Table<a class="headerlink" href="#table" title="Permalink to this heading">#</a></h2>
 <p>A <a class="reference external" href="https://arrow.apache.org/docs/java/reference/org/apache/arrow/vector/table/Table.html">Table</a> is an immutable tabular data structure, very similar to VectorSchemaRoot, in that it is also built on ValueVectors and schemas. Unlike VectorSchemaRoot, Table is not designed for batch processing. Here is a version of the example above, showing how to create a Table, rather than a VectorSchemaRoot:</p>
 <div class="highlight-Java notranslate"><div class="highlight"><pre><span></span><span class="n">BitVector</span><span class="w"> </span><span class="n">bitVector</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">BitVector</span><span class="p">(</span><span class="s">&quot;boolean&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">allocator</span><span class="p">);</span>
 <span class="n">VarCharVector</span><span class="w"> </span><span class="n">varCharVector</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">VarCharVector</span><span class="p">(</span><span class="s">&quot;varchar&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">allocator</span><span class="p">);</span>
 <span class="n">bitVector</span><span class="p">.</span><span class="na">allocateNew</span><span class="p">();</span>
 <span class="n">varCharVector</span><span class="p">.</span><span class="na">allocateNew</span><span class="p">();</span>
 <span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">10</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="o">++</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
 <span class="w">  </span><span class="n">bitVector</span><span class="p">.</span><span class="na">setSafe</span><span class="p">(</span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">%</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">?</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="mi">1</span><span class="p">);</span>
 <span class="w">  </span><span class="n">varCharVector</span><span class="p">.</span><span class="na">setSafe</span><span class="p">(</span><span class="n">i</span><span class="p">,</span><span class="w"> </span><span class="p">(</span><span class="s">&quot;test&quot;</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">i</span><span class="p">).</span><span class="na">getBytes</span><span class="p">(</span><span class="n">StandardCharsets</span><span class="p">.</span><span class="na">UTF_8</span><span class="p">));</span>
 <span class="p">}</span>
 <span class="n">bitVector</span><span class="p">.</span><span class="na">setValueCount</span><span class="p">(</span><span class="mi">10</span><span class="p">);</span>
 <span class="n">varCharVector</span><span class="p">.</span><span class="na">setValueCount</span><span class="p">(</span><span class="mi">10</span><span class="p">);</span>

 <span class="n">List</span><span class="o">&lt;</span><span class="n">FieldVector</span><span class="o">&gt;</span><span class="w"> </span><span class="n">vectors</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">Arrays</span><span class="p">.</span><span class="na">asList</span><span class="p">(</span><span class="n">bitVector</span><span class="p">,</span><span class="w"> </span><span class="n">varCharVector</span><span class="p">);</span>
 <span class="n">Table</span><span class="w"> </span><span class="n">table</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">Table</span><span class="p">(</span><span class="n">vectors</span><span class="p">);</span>
 </pre></div>
 </div>
 <p>See the <a class="reference internal" href="table.html"><span class="doc">Table</span></a> documentation for more information.</p>
 </section>
 </section>


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