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| <section id="arrow-compute"> |
| <h1>Arrow Compute<a class="headerlink" href="#arrow-compute" title="Permalink to this heading">#</a></h1> |
| <p>Apache Arrow provides compute functions to facilitate efficient and |
| portable data processing. In this article, you will use Arrow’s compute |
| functionality to:</p> |
| <ol class="arabic simple"> |
| <li><p>Calculate a sum over a column</p></li> |
| <li><p>Calculate element-wise sums over two columns</p></li> |
| <li><p>Search for a value in a column</p></li> |
| </ol> |
| <section id="pre-requisites"> |
| <h2>Pre-requisites<a class="headerlink" href="#pre-requisites" title="Permalink to this heading">#</a></h2> |
| <p>Before continuing, make sure you have:</p> |
| <ol class="arabic simple"> |
| <li><p>An Arrow installation, which you can set up here: <a class="reference internal" href="../build_system.html"><span class="doc">Using Arrow C++ in your own project</span></a></p></li> |
| <li><p>An understanding of basic Arrow data structures from <a class="reference internal" href="basic_arrow.html"><span class="doc">Basic Arrow Data Structures</span></a></p></li> |
| </ol> |
| </section> |
| <section id="setup"> |
| <h2>Setup<a class="headerlink" href="#setup" title="Permalink to this heading">#</a></h2> |
| <p>Before running some computations, we need to fill in a couple gaps:</p> |
| <ol class="arabic simple"> |
| <li><p>We need to include necessary headers.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">A</span> <span class="pre">main()</span></code> is needed to glue things together.</p></li> |
| <li><p>We need data to play with.</p></li> |
| </ol> |
| <section id="includes"> |
| <h3>Includes<a class="headerlink" href="#includes" title="Permalink to this heading">#</a></h3> |
| <p>Before writing C++ code, we need some includes. We’ll get <code class="docutils literal notranslate"><span class="pre">iostream</span></code> for output, then import Arrow’s |
| compute functionality:</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/api.h></span> |
| <span class="cp">#include</span><span class="w"> </span><span class="cpf"><arrow/compute/api.h></span> |
| |
| <span class="cp">#include</span><span class="w"> </span><span class="cpf"><iostream></span> |
| </pre></div> |
| </div> |
| </section> |
| <section id="main"> |
| <h3>Main()<a class="headerlink" href="#main" title="Permalink to this heading">#</a></h3> |
| <p>For our glue, we’ll use the <code class="docutils literal notranslate"><span class="pre">main()</span></code> pattern from the previous tutorial on |
| data structures:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span><span class="w"> </span><span class="p">{</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">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RunMain</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">st</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="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">st</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="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span> |
| <span class="w"> </span><span class="p">}</span> |
| <span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span> |
| <span class="p">}</span> |
| </pre></div> |
| </div> |
| <p>Which, like when we used it before, is paired with a <code class="docutils literal notranslate"><span class="pre">RunMain()</span></code>:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="n">arrow</span><span class="o">::</span><span class="n">Status</span><span class="w"> </span><span class="nf">RunMain</span><span class="p">()</span><span class="w"> </span><span class="p">{</span> |
| </pre></div> |
| </div> |
| </section> |
| <section id="generating-tables-for-computation"> |
| <h3>Generating Tables for Computation<a class="headerlink" href="#generating-tables-for-computation" title="Permalink to this heading">#</a></h3> |
| <p>Before we begin, we’ll initialize 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">Table</span></code></a> with two columns to play with. We’ll use |
| the method from <a class="reference internal" href="basic_arrow.html"><span class="doc">Basic Arrow Data Structures</span></a>, so look back |
| there if anything’s confusing:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="c1">// Create a couple 32-bit integer arrays.</span> |
| <span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">Int32Builder</span><span class="w"> </span><span class="n">int32builder</span><span class="p">;</span> |
| <span class="w"> </span><span class="kt">int32_t</span><span class="w"> </span><span class="n">some_nums_raw</span><span class="p">[</span><span class="mi">5</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span><span class="mi">34</span><span class="p">,</span><span class="w"> </span><span class="mi">624</span><span class="p">,</span><span class="w"> </span><span class="mi">2223</span><span class="p">,</span><span class="w"> </span><span class="mi">5654</span><span class="p">,</span><span class="w"> </span><span class="mi">4356</span><span class="p">};</span> |
| <span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">int32builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">(</span><span class="n">some_nums_raw</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">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">some_nums</span><span class="p">;</span> |
| <span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">some_nums</span><span class="p">,</span><span class="w"> </span><span class="n">int32builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">());</span> |
| |
| <span class="w"> </span><span class="kt">int32_t</span><span class="w"> </span><span class="n">more_nums_raw</span><span class="p">[</span><span class="mi">5</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span><span class="mi">75342</span><span class="p">,</span><span class="w"> </span><span class="mi">23</span><span class="p">,</span><span class="w"> </span><span class="mi">64</span><span class="p">,</span><span class="w"> </span><span class="mi">17</span><span class="p">,</span><span class="w"> </span><span class="mi">736</span><span class="p">};</span> |
| <span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">int32builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">(</span><span class="n">more_nums_raw</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">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">more_nums</span><span class="p">;</span> |
| <span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">more_nums</span><span class="p">,</span><span class="w"> </span><span class="n">int32builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">());</span> |
| |
| <span class="w"> </span><span class="c1">// Make a table out of our pair of arrays.</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">Field</span><span class="o">></span><span class="w"> </span><span class="n">field_a</span><span class="p">,</span><span class="w"> </span><span class="n">field_b</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">Schema</span><span class="o">></span><span class="w"> </span><span class="n">schema</span><span class="p">;</span> |
| |
| <span class="w"> </span><span class="n">field_a</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">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">int32</span><span class="p">());</span> |
| <span class="w"> </span><span class="n">field_b</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">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">int32</span><span class="p">());</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="n">field_a</span><span class="p">,</span><span class="w"> </span><span class="n">field_b</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="p">;</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="p">{</span><span class="n">some_nums</span><span class="p">,</span><span class="w"> </span><span class="n">more_nums</span><span class="p">},</span><span class="w"> </span><span class="mi">5</span><span class="p">);</span> |
| </pre></div> |
| </div> |
| </section> |
| </section> |
| <section id="calculating-a-sum-over-an-array"> |
| <h2>Calculating a Sum over an Array<a class="headerlink" href="#calculating-a-sum-over-an-array" title="Permalink to this heading">#</a></h2> |
| <p>Using a computation function has two general steps, which we separate |
| here:</p> |
| <ol class="arabic simple"> |
| <li><p>Preparing a <a class="reference internal" href="../api/compute.html#_CPPv4N5arrow5DatumE" title="arrow::Datum"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Datum</span></code></a> for output</p></li> |
| <li><p>Calling <code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">compute::Sum()</span></code>, a convenience function for summation over an <a class="reference internal" href="../api/array.html#_CPPv4N5arrow5ArrayE" title="arrow::Array"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Array</span></code></a></p></li> |
| <li><p>Retrieving and printing output</p></li> |
| </ol> |
| <section id="prepare-memory-for-output-with-datum"> |
| <h3>Prepare Memory for Output with Datum<a class="headerlink" href="#prepare-memory-for-output-with-datum" title="Permalink to this heading">#</a></h3> |
| <p>When computation is done, we need somewhere for our results to go. In |
| Arrow, the object for such output is called <a class="reference internal" href="../api/compute.html#_CPPv4N5arrow5DatumE" title="arrow::Datum"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Datum</span></code></a>. This object is used |
| to pass around inputs and outputs in compute functions, and can contain |
| many differently-shaped Arrow data structures. We’ll need it to retrieve |
| the output from compute functions.</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="c1">// The Datum class is what all compute functions output to, and they can take Datums</span> |
| <span class="w"> </span><span class="c1">// as inputs, as well.</span> |
| <span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">Datum</span><span class="w"> </span><span class="n">sum</span><span class="p">;</span> |
| </pre></div> |
| </div> |
| </section> |
| <section id="call-sum"> |
| <h3>Call Sum()<a class="headerlink" href="#call-sum" title="Permalink to this heading">#</a></h3> |
| <p>Here, we’ll get our <a class="reference internal" href="../api/table.html#_CPPv4N5arrow5TableE" title="arrow::Table"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Table</span></code></a>, which has columns “A” and “B”, and sum over |
| column “A.” For summation, there is a convenience function, called |
| <code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">compute::Sum()</span></code>, which reduces the complexity of the compute interface. We’ll look |
| at the more complex version for the next computation. For a given |
| function, refer to <a class="reference internal" href="../api/compute.html"><span class="doc">Compute Functions</span></a> to see if there is a |
| convenience function. <code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">compute::Sum()</span></code> takes in a given <a class="reference internal" href="../api/array.html#_CPPv4N5arrow5ArrayE" title="arrow::Array"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Array</span></code></a> or <a class="reference internal" href="../api/array.html#_CPPv4N5arrow12ChunkedArrayE" title="arrow::ChunkedArray"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">ChunkedArray</span></code></a> |
| – here, we use <a class="reference internal" href="../api/table.html#_CPPv4NK5arrow5Table15GetColumnByNameERKNSt6stringE" title="arrow::Table::GetColumnByName"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">Table::GetColumnByName()</span></code></a> to pass in column A. Then, it outputs to |
| a <a class="reference internal" href="../api/compute.html#_CPPv4N5arrow5DatumE" title="arrow::Datum"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Datum</span></code></a>. Putting that all together, we get this:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="c1">// Here, we can use arrow::compute::Sum. This is a convenience function, and the next</span> |
| <span class="w"> </span><span class="c1">// computation won't be so simple. However, using these where possible helps</span> |
| <span class="w"> </span><span class="c1">// readability.</span> |
| <span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">sum</span><span class="p">,</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">Sum</span><span class="p">({</span><span class="n">table</span><span class="o">-></span><span class="n">GetColumnByName</span><span class="p">(</span><span class="s">"A"</span><span class="p">)}));</span> |
| </pre></div> |
| </div> |
| </section> |
| <section id="get-results-from-datum"> |
| <h3>Get Results from Datum<a class="headerlink" href="#get-results-from-datum" title="Permalink to this heading">#</a></h3> |
| <p>The previous step leaves us with a <a class="reference internal" href="../api/compute.html#_CPPv4N5arrow5DatumE" title="arrow::Datum"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Datum</span></code></a> which contains our sum. |
| However, we cannot print it directly – its flexibility in holding |
| arbitrary Arrow data structures means we have to retrieve our data |
| carefully. First, to understand what’s in it, we can check which kind of |
| data structure it is, then what kind of primitive is being held:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="c1">// Get the kind of Datum and what it holds -- this is a Scalar, with int64.</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">"Datum kind: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">sum</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="s">" content type: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">sum</span><span class="p">.</span><span class="n">type</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>This should report the <a class="reference internal" href="../api/compute.html#_CPPv4N5arrow5DatumE" title="arrow::Datum"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Datum</span></code></a> stores a <a class="reference internal" href="../api/scalar.html#_CPPv4N5arrow6ScalarE" title="arrow::Scalar"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Scalar</span></code></a> with a 64-bit integer. Just |
| to see what the value is, we can print it out like so, which yields |
| 12891:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="c1">// Note that we explicitly request a scalar -- the Datum cannot simply give what it is,</span> |
| <span class="w"> </span><span class="c1">// you must ask for the correct type.</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">sum</span><span class="p">.</span><span class="n">scalar_as</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Int64Scalar</span><span class="o">></span><span class="p">().</span><span class="n">value</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>Now we’ve used <code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">compute::Sum()</span></code> and gotten what we want out of it!</p> |
| </section> |
| </section> |
| <section id="calculating-element-wise-array-addition-with-callfunction"> |
| <h2>Calculating Element-Wise Array Addition with CallFunction()<a class="headerlink" href="#calculating-element-wise-array-addition-with-callfunction" title="Permalink to this heading">#</a></h2> |
| <p>A next layer of complexity uses what <code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">compute::Sum()</span></code> was helpfully hiding: |
| <code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">compute::CallFunction()</span></code>. For this example, we will explore how to use the more |
| robust <code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">compute::CallFunction()</span></code> with the “add” compute function. The pattern |
| remains similar:</p> |
| <ol class="arabic simple"> |
| <li><p>Preparing a Datum for output</p></li> |
| <li><p>Calling <code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">compute::CallFunction()</span></code> with “add”</p></li> |
| <li><p>Retrieving and printing output</p></li> |
| </ol> |
| <section id="id1"> |
| <h3>Prepare Memory for Output with Datum<a class="headerlink" href="#id1" title="Permalink to this heading">#</a></h3> |
| <p>Once more, we’ll need a Datum for any output we get:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">Datum</span><span class="w"> </span><span class="n">element_wise_sum</span><span class="p">;</span> |
| </pre></div> |
| </div> |
| </section> |
| <section id="use-callfunction-with-add"> |
| <h3>Use CallFunction() with “add”<a class="headerlink" href="#use-callfunction-with-add" title="Permalink to this heading">#</a></h3> |
| <p><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">compute::CallFunction()</span></code> takes the name of the desired function as its first |
| argument, then the data inputs for said function as a vector in its |
| second argument. Right now, we want an element-wise addition between |
| columns “A” and “B”. So, we’ll ask for “add,” pass in columns “A and B”, |
| and output to our <a class="reference internal" href="../api/compute.html#_CPPv4N5arrow5DatumE" title="arrow::Datum"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Datum</span></code></a>. Put this all together, and we get:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="c1">// Get element-wise sum of both columns A and B in our Table. Note that here we use</span> |
| <span class="w"> </span><span class="c1">// CallFunction(), which takes the name of the function as the first argument.</span> |
| <span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">element_wise_sum</span><span class="p">,</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">CallFunction</span><span class="p">(</span> |
| <span class="w"> </span><span class="s">"add"</span><span class="p">,</span><span class="w"> </span><span class="p">{</span><span class="n">table</span><span class="o">-></span><span class="n">GetColumnByName</span><span class="p">(</span><span class="s">"A"</span><span class="p">),</span> |
| <span class="w"> </span><span class="n">table</span><span class="o">-></span><span class="n">GetColumnByName</span><span class="p">(</span><span class="s">"B"</span><span class="p">)}));</span> |
| </pre></div> |
| </div> |
| <div class="admonition seealso"> |
| <p class="admonition-title">See also</p> |
| <p><a class="reference internal" href="../compute.html#compute-function-list"><span class="std std-ref">Available functions</span></a> for a list of other functions to go with <code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">compute::CallFunction()</span></code></p> |
| </div> |
| </section> |
| <section id="id2"> |
| <h3>Get Results from Datum<a class="headerlink" href="#id2" title="Permalink to this heading">#</a></h3> |
| <p>Again, the <a class="reference internal" href="../api/compute.html#_CPPv4N5arrow5DatumE" title="arrow::Datum"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Datum</span></code></a> needs some careful handling. Said handling is much |
| easier when we know what’s in it. This <a class="reference internal" href="../api/compute.html#_CPPv4N5arrow5DatumE" title="arrow::Datum"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Datum</span></code></a> holds a <a class="reference internal" href="../api/array.html#_CPPv4N5arrow12ChunkedArrayE" title="arrow::ChunkedArray"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">ChunkedArray</span></code></a> with |
| 32-bit integers, but we can print that to confirm:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="c1">// Get the kind of Datum and what it holds -- this is a ChunkedArray, with int32.</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">"Datum kind: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">element_wise_sum</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="s">" content type: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">element_wise_sum</span><span class="p">.</span><span class="n">type</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>Since it’s a <a class="reference internal" href="../api/array.html#_CPPv4N5arrow12ChunkedArrayE" title="arrow::ChunkedArray"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">ChunkedArray</span></code></a>, we request that from the <a class="reference internal" href="../api/compute.html#_CPPv4N5arrow5DatumE" title="arrow::Datum"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Datum</span></code></a> – <a class="reference internal" href="../api/array.html#_CPPv4N5arrow12ChunkedArrayE" title="arrow::ChunkedArray"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">ChunkedArray</span></code></a> |
| has a <a class="reference internal" href="../api/array.html#_CPPv4NK5arrow12ChunkedArray8ToStringEv" title="arrow::ChunkedArray::ToString"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">ChunkedArray::ToString()</span></code></a> method, so we’ll use that to print out its contents:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="c1">// This time, we get a ChunkedArray, not a scalar.</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">element_wise_sum</span><span class="p">.</span><span class="n">chunked_array</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>The output looks like this:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="n">Datum</span><span class="w"> </span><span class="n">kind</span><span class="o">:</span><span class="w"> </span><span class="n">ChunkedArray</span><span class="w"> </span><span class="n">content</span><span class="w"> </span><span class="n">type</span><span class="o">:</span><span class="w"> </span><span class="n">int32</span> |
| <span class="p">[</span> |
| <span class="w"> </span><span class="p">[</span> |
| <span class="w"> </span><span class="mi">75376</span><span class="p">,</span> |
| <span class="w"> </span><span class="mi">647</span><span class="p">,</span> |
| <span class="w"> </span><span class="mi">2287</span><span class="p">,</span> |
| <span class="w"> </span><span class="mi">5671</span><span class="p">,</span> |
| <span class="w"> </span><span class="mi">5092</span> |
| <span class="w"> </span><span class="p">]</span> |
| <span class="p">]</span> |
| </pre></div> |
| </div> |
| <p>Now, we’ve used <code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">compute::CallFunction()</span></code>, instead of a convenience function! This |
| enables a much wider range of available computations.</p> |
| </section> |
| </section> |
| <section id="searching-for-a-value-with-callfunction-and-options"> |
| <h2>Searching for a Value with CallFunction() and Options<a class="headerlink" href="#searching-for-a-value-with-callfunction-and-options" title="Permalink to this heading">#</a></h2> |
| <p>One class of computations remains. <code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">compute::CallFunction()</span></code> uses a vector for data |
| inputs, but computation often needs additional arguments to function. In |
| order to supply this, computation functions may be associated with |
| structs where their arguments can be defined. You can check a given |
| function to see which struct it uses <a class="reference internal" href="../compute.html#compute-function-list"><span class="std std-ref">here</span></a>. For this example, we’ll search for a value in column “A” using |
| the “index” compute function. This process has three steps, as opposed |
| to the two from before:</p> |
| <ol class="arabic simple"> |
| <li><p>Preparing a <a class="reference internal" href="../api/compute.html#_CPPv4N5arrow5DatumE" title="arrow::Datum"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Datum</span></code></a> for output</p></li> |
| <li><p>Preparing <a class="reference internal" href="../api/compute.html#_CPPv4N5arrow7compute12IndexOptionsE" title="arrow::compute::IndexOptions"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">compute::IndexOptions</span></code></a></p></li> |
| <li><p>Calling <code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">compute::CallFunction()</span></code> with “index” and <a class="reference internal" href="../api/compute.html#_CPPv4N5arrow7compute12IndexOptionsE" title="arrow::compute::IndexOptions"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">compute::IndexOptions</span></code></a></p></li> |
| <li><p>Retrieving and printing output</p></li> |
| </ol> |
| <section id="id3"> |
| <h3>Prepare Memory for Output with Datum<a class="headerlink" href="#id3" title="Permalink to this heading">#</a></h3> |
| <p>We’ll need a <a class="reference internal" href="../api/compute.html#_CPPv4N5arrow5DatumE" title="arrow::Datum"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Datum</span></code></a> for any output we get:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="c1">// Use an options struct to set up searching for 2223 in column A (the third item).</span> |
| <span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">Datum</span><span class="w"> </span><span class="n">third_item</span><span class="p">;</span> |
| </pre></div> |
| </div> |
| </section> |
| <section id="configure-index-with-indexoptions"> |
| <h3>Configure “index” with IndexOptions<a class="headerlink" href="#configure-index-with-indexoptions" title="Permalink to this heading">#</a></h3> |
| <p>For this exploration, we’ll use the “index” function – this is a |
| searching method, which returns the index of an input value. In order to |
| pass this input value, we require an <a class="reference internal" href="../api/compute.html#_CPPv4N5arrow7compute12IndexOptionsE" title="arrow::compute::IndexOptions"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">compute::IndexOptions</span></code></a> struct. So, let’s make |
| that struct:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="c1">// An options struct is used in lieu of passing an arbitrary amount of arguments.</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">IndexOptions</span><span class="w"> </span><span class="n">index_options</span><span class="p">;</span> |
| </pre></div> |
| </div> |
| <p>In a searching function, one requires a target value. Here, we’ll use |
| 2223, the third item in column A, and configure our struct accordingly:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="c1">// We need an Arrow Scalar, not a raw value.</span> |
| <span class="w"> </span><span class="n">index_options</span><span class="p">.</span><span class="n">value</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">MakeScalar</span><span class="p">(</span><span class="mi">2223</span><span class="p">);</span> |
| </pre></div> |
| </div> |
| </section> |
| <section id="use-callfunction-with-index-and-indexoptions"> |
| <h3>Use CallFunction() with “index” and IndexOptions<a class="headerlink" href="#use-callfunction-with-index-and-indexoptions" title="Permalink to this heading">#</a></h3> |
| <p>To actually run the function, we use <code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">compute::CallFunction()</span></code> again, this time |
| passing our IndexOptions struct by reference as a third argument. As |
| before, the first argument is the name of the function, and the second |
| our data input:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span> |
| <span class="w"> </span><span class="n">third_item</span><span class="p">,</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">CallFunction</span><span class="p">(</span><span class="s">"index"</span><span class="p">,</span><span class="w"> </span><span class="p">{</span><span class="n">table</span><span class="o">-></span><span class="n">GetColumnByName</span><span class="p">(</span><span class="s">"A"</span><span class="p">)},</span> |
| <span class="w"> </span><span class="o">&</span><span class="n">index_options</span><span class="p">));</span> |
| </pre></div> |
| </div> |
| </section> |
| <section id="id4"> |
| <h3>Get Results from Datum<a class="headerlink" href="#id4" title="Permalink to this heading">#</a></h3> |
| <p>One last time, let’s see what our <a class="reference internal" href="../api/compute.html#_CPPv4N5arrow5DatumE" title="arrow::Datum"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Datum</span></code></a> has! This will be a <a class="reference internal" href="../api/scalar.html#_CPPv4N5arrow6ScalarE" title="arrow::Scalar"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Scalar</span></code></a> with |
| a 64-bit integer, and the output will be 2:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="c1">// Get the kind of Datum and what it holds -- this is a Scalar, with int64</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">"Datum kind: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">third_item</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="s">" content type: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">third_item</span><span class="p">.</span><span class="n">type</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="w"> </span><span class="c1">// We get a scalar -- the location of 2223 in column A, which is 2 in 0-based indexing.</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">third_item</span><span class="p">.</span><span class="n">scalar_as</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Int64Scalar</span><span class="o">></span><span class="p">().</span><span class="n">value</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> |
| </section> |
| </section> |
| <section id="ending-program"> |
| <h2>Ending Program<a class="headerlink" href="#ending-program" title="Permalink to this heading">#</a></h2> |
| <p>At the end, we just return <a class="reference internal" href="../api/support.html#_CPPv4N5arrow6Status2OKEv" title="arrow::Status::OK"><code class="xref cpp cpp-func docutils literal notranslate"><span class="pre">arrow::Status::OK()</span></code></a>, so the <code class="docutils literal notranslate"><span class="pre">main()</span></code> knows that |
| we’re done, and that everything’s okay, just like the preceding |
| tutorials.</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></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="p">}</span> |
| </pre></div> |
| </div> |
| <p>With that, you’ve used compute functions which fall into the three main |
| types – with and without convenience functions, then with an Options |
| struct. Now you can process any <a class="reference internal" href="../api/table.html#_CPPv4N5arrow5TableE" title="arrow::Table"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Table</span></code></a> you need to, and solve whatever |
| data problem you have that fits into memory!</p> |
| <p>Which means that now we have to see how we can work with |
| larger-than-memory datasets, via Arrow Datasets in the next article.</p> |
| <p>Refer to the below for a copy of the complete code:</p> |
| <div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="linenos"> 19</span><span class="c1">// (Doc section: Includes)</span> |
| <span class="linenos"> 20</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><arrow/api.h></span> |
| <span class="linenos"> 21</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><arrow/compute/api.h></span> |
| <span class="linenos"> 22</span> |
| <span class="linenos"> 23</span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><iostream></span> |
| <span class="linenos"> 24</span><span class="c1">// (Doc section: Includes)</span> |
| <span class="linenos"> 25</span> |
| <span class="linenos"> 26</span><span class="c1">// (Doc section: RunMain)</span> |
| <span class="linenos"> 27</span><span class="n">arrow</span><span class="o">::</span><span class="n">Status</span><span class="w"> </span><span class="nf">RunMain</span><span class="p">()</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos"> 28</span><span class="w"> </span><span class="c1">// (Doc section: RunMain)</span> |
| <span class="linenos"> 29</span><span class="w"> </span><span class="c1">// (Doc section: Create Tables)</span> |
| <span class="linenos"> 30</span><span class="w"> </span><span class="c1">// Create a couple 32-bit integer arrays.</span> |
| <span class="linenos"> 31</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">Int32Builder</span><span class="w"> </span><span class="n">int32builder</span><span class="p">;</span> |
| <span class="linenos"> 32</span><span class="w"> </span><span class="kt">int32_t</span><span class="w"> </span><span class="n">some_nums_raw</span><span class="p">[</span><span class="mi">5</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span><span class="mi">34</span><span class="p">,</span><span class="w"> </span><span class="mi">624</span><span class="p">,</span><span class="w"> </span><span class="mi">2223</span><span class="p">,</span><span class="w"> </span><span class="mi">5654</span><span class="p">,</span><span class="w"> </span><span class="mi">4356</span><span class="p">};</span> |
| <span class="linenos"> 33</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">int32builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">(</span><span class="n">some_nums_raw</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">));</span> |
| <span class="linenos"> 34</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">some_nums</span><span class="p">;</span> |
| <span class="linenos"> 35</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">some_nums</span><span class="p">,</span><span class="w"> </span><span class="n">int32builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos"> 36</span> |
| <span class="linenos"> 37</span><span class="w"> </span><span class="kt">int32_t</span><span class="w"> </span><span class="n">more_nums_raw</span><span class="p">[</span><span class="mi">5</span><span class="p">]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span><span class="mi">75342</span><span class="p">,</span><span class="w"> </span><span class="mi">23</span><span class="p">,</span><span class="w"> </span><span class="mi">64</span><span class="p">,</span><span class="w"> </span><span class="mi">17</span><span class="p">,</span><span class="w"> </span><span class="mi">736</span><span class="p">};</span> |
| <span class="linenos"> 38</span><span class="w"> </span><span class="n">ARROW_RETURN_NOT_OK</span><span class="p">(</span><span class="n">int32builder</span><span class="p">.</span><span class="n">AppendValues</span><span class="p">(</span><span class="n">more_nums_raw</span><span class="p">,</span><span class="w"> </span><span class="mi">5</span><span class="p">));</span> |
| <span class="linenos"> 39</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">more_nums</span><span class="p">;</span> |
| <span class="linenos"> 40</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">more_nums</span><span class="p">,</span><span class="w"> </span><span class="n">int32builder</span><span class="p">.</span><span class="n">Finish</span><span class="p">());</span> |
| <span class="linenos"> 41</span> |
| <span class="linenos"> 42</span><span class="w"> </span><span class="c1">// Make a table out of our pair of arrays.</span> |
| <span class="linenos"> 43</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">Field</span><span class="o">></span><span class="w"> </span><span class="n">field_a</span><span class="p">,</span><span class="w"> </span><span class="n">field_b</span><span class="p">;</span> |
| <span class="linenos"> 44</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">Schema</span><span class="o">></span><span class="w"> </span><span class="n">schema</span><span class="p">;</span> |
| <span class="linenos"> 45</span> |
| <span class="linenos"> 46</span><span class="w"> </span><span class="n">field_a</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">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">int32</span><span class="p">());</span> |
| <span class="linenos"> 47</span><span class="w"> </span><span class="n">field_b</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">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">int32</span><span class="p">());</span> |
| <span class="linenos"> 48</span> |
| <span class="linenos"> 49</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="n">field_a</span><span class="p">,</span><span class="w"> </span><span class="n">field_b</span><span class="p">});</span> |
| <span class="linenos"> 50</span> |
| <span class="linenos"> 51</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"> 52</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="p">{</span><span class="n">some_nums</span><span class="p">,</span><span class="w"> </span><span class="n">more_nums</span><span class="p">},</span><span class="w"> </span><span class="mi">5</span><span class="p">);</span> |
| <span class="linenos"> 53</span><span class="w"> </span><span class="c1">// (Doc section: Create Tables)</span> |
| <span class="linenos"> 54</span> |
| <span class="linenos"> 55</span><span class="w"> </span><span class="c1">// (Doc section: Sum Datum Declaration)</span> |
| <span class="linenos"> 56</span><span class="w"> </span><span class="c1">// The Datum class is what all compute functions output to, and they can take Datums</span> |
| <span class="linenos"> 57</span><span class="w"> </span><span class="c1">// as inputs, as well.</span> |
| <span class="linenos"> 58</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">Datum</span><span class="w"> </span><span class="n">sum</span><span class="p">;</span> |
| <span class="linenos"> 59</span><span class="w"> </span><span class="c1">// (Doc section: Sum Datum Declaration)</span> |
| <span class="linenos"> 60</span><span class="w"> </span><span class="c1">// (Doc section: Sum Call)</span> |
| <span class="linenos"> 61</span><span class="w"> </span><span class="c1">// Here, we can use arrow::compute::Sum. This is a convenience function, and the next</span> |
| <span class="linenos"> 62</span><span class="w"> </span><span class="c1">// computation won't be so simple. However, using these where possible helps</span> |
| <span class="linenos"> 63</span><span class="w"> </span><span class="c1">// readability.</span> |
| <span class="linenos"> 64</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">sum</span><span class="p">,</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">Sum</span><span class="p">({</span><span class="n">table</span><span class="o">-></span><span class="n">GetColumnByName</span><span class="p">(</span><span class="s">"A"</span><span class="p">)}));</span> |
| <span class="linenos"> 65</span><span class="w"> </span><span class="c1">// (Doc section: Sum Call)</span> |
| <span class="linenos"> 66</span><span class="w"> </span><span class="c1">// (Doc section: Sum Datum Type)</span> |
| <span class="linenos"> 67</span><span class="w"> </span><span class="c1">// Get the kind of Datum and what it holds -- this is a Scalar, with int64.</span> |
| <span class="linenos"> 68</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">"Datum kind: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">sum</span><span class="p">.</span><span class="n">ToString</span><span class="p">()</span> |
| <span class="linenos"> 69</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">" content type: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">sum</span><span class="p">.</span><span class="n">type</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"> 70</span><span class="w"> </span><span class="c1">// (Doc section: Sum Datum Type)</span> |
| <span class="linenos"> 71</span><span class="w"> </span><span class="c1">// (Doc section: Sum Contents)</span> |
| <span class="linenos"> 72</span><span class="w"> </span><span class="c1">// Note that we explicitly request a scalar -- the Datum cannot simply give what it is,</span> |
| <span class="linenos"> 73</span><span class="w"> </span><span class="c1">// you must ask for the correct type.</span> |
| <span class="linenos"> 74</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">sum</span><span class="p">.</span><span class="n">scalar_as</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Int64Scalar</span><span class="o">></span><span class="p">().</span><span class="n">value</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"> 75</span><span class="w"> </span><span class="c1">// (Doc section: Sum Contents)</span> |
| <span class="linenos"> 76</span> |
| <span class="linenos"> 77</span><span class="w"> </span><span class="c1">// (Doc section: Add Datum Declaration)</span> |
| <span class="linenos"> 78</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">Datum</span><span class="w"> </span><span class="n">element_wise_sum</span><span class="p">;</span> |
| <span class="linenos"> 79</span><span class="w"> </span><span class="c1">// (Doc section: Add Datum Declaration)</span> |
| <span class="linenos"> 80</span><span class="w"> </span><span class="c1">// (Doc section: Add Call)</span> |
| <span class="linenos"> 81</span><span class="w"> </span><span class="c1">// Get element-wise sum of both columns A and B in our Table. Note that here we use</span> |
| <span class="linenos"> 82</span><span class="w"> </span><span class="c1">// CallFunction(), which takes the name of the function as the first argument.</span> |
| <span class="linenos"> 83</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">element_wise_sum</span><span class="p">,</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">CallFunction</span><span class="p">(</span> |
| <span class="linenos"> 84</span><span class="w"> </span><span class="s">"add"</span><span class="p">,</span><span class="w"> </span><span class="p">{</span><span class="n">table</span><span class="o">-></span><span class="n">GetColumnByName</span><span class="p">(</span><span class="s">"A"</span><span class="p">),</span> |
| <span class="linenos"> 85</span><span class="w"> </span><span class="n">table</span><span class="o">-></span><span class="n">GetColumnByName</span><span class="p">(</span><span class="s">"B"</span><span class="p">)}));</span> |
| <span class="linenos"> 86</span><span class="w"> </span><span class="c1">// (Doc section: Add Call)</span> |
| <span class="linenos"> 87</span><span class="w"> </span><span class="c1">// (Doc section: Add Datum Type)</span> |
| <span class="linenos"> 88</span><span class="w"> </span><span class="c1">// Get the kind of Datum and what it holds -- this is a ChunkedArray, with int32.</span> |
| <span class="linenos"> 89</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">"Datum kind: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">element_wise_sum</span><span class="p">.</span><span class="n">ToString</span><span class="p">()</span> |
| <span class="linenos"> 90</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">" content type: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">element_wise_sum</span><span class="p">.</span><span class="n">type</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"> 91</span><span class="w"> </span><span class="c1">// (Doc section: Add Datum Type)</span> |
| <span class="linenos"> 92</span><span class="w"> </span><span class="c1">// (Doc section: Add Contents)</span> |
| <span class="linenos"> 93</span><span class="w"> </span><span class="c1">// This time, we get a ChunkedArray, not a scalar.</span> |
| <span class="linenos"> 94</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">element_wise_sum</span><span class="p">.</span><span class="n">chunked_array</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"> 95</span><span class="w"> </span><span class="c1">// (Doc section: Add Contents)</span> |
| <span class="linenos"> 96</span> |
| <span class="linenos"> 97</span><span class="w"> </span><span class="c1">// (Doc section: Index Datum Declare)</span> |
| <span class="linenos"> 98</span><span class="w"> </span><span class="c1">// Use an options struct to set up searching for 2223 in column A (the third item).</span> |
| <span class="linenos"> 99</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">Datum</span><span class="w"> </span><span class="n">third_item</span><span class="p">;</span> |
| <span class="linenos">100</span><span class="w"> </span><span class="c1">// (Doc section: Index Datum Declare)</span> |
| <span class="linenos">101</span><span class="w"> </span><span class="c1">// (Doc section: IndexOptions Declare)</span> |
| <span class="linenos">102</span><span class="w"> </span><span class="c1">// An options struct is used in lieu of passing an arbitrary amount of arguments.</span> |
| <span class="linenos">103</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">IndexOptions</span><span class="w"> </span><span class="n">index_options</span><span class="p">;</span> |
| <span class="linenos">104</span><span class="w"> </span><span class="c1">// (Doc section: IndexOptions Declare)</span> |
| <span class="linenos">105</span><span class="w"> </span><span class="c1">// (Doc section: IndexOptions Assign)</span> |
| <span class="linenos">106</span><span class="w"> </span><span class="c1">// We need an Arrow Scalar, not a raw value.</span> |
| <span class="linenos">107</span><span class="w"> </span><span class="n">index_options</span><span class="p">.</span><span class="n">value</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">MakeScalar</span><span class="p">(</span><span class="mi">2223</span><span class="p">);</span> |
| <span class="linenos">108</span><span class="w"> </span><span class="c1">// (Doc section: IndexOptions Assign)</span> |
| <span class="linenos">109</span><span class="w"> </span><span class="c1">// (Doc section: Index Call)</span> |
| <span class="linenos">110</span><span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span> |
| <span class="linenos">111</span><span class="w"> </span><span class="n">third_item</span><span class="p">,</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">CallFunction</span><span class="p">(</span><span class="s">"index"</span><span class="p">,</span><span class="w"> </span><span class="p">{</span><span class="n">table</span><span class="o">-></span><span class="n">GetColumnByName</span><span class="p">(</span><span class="s">"A"</span><span class="p">)},</span> |
| <span class="linenos">112</span><span class="w"> </span><span class="o">&</span><span class="n">index_options</span><span class="p">));</span> |
| <span class="linenos">113</span><span class="w"> </span><span class="c1">// (Doc section: Index Call)</span> |
| <span class="linenos">114</span><span class="w"> </span><span class="c1">// (Doc section: Index Inspection)</span> |
| <span class="linenos">115</span><span class="w"> </span><span class="c1">// Get the kind of Datum and what it holds -- this is a Scalar, with int64</span> |
| <span class="linenos">116</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">"Datum kind: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">third_item</span><span class="p">.</span><span class="n">ToString</span><span class="p">()</span> |
| <span class="linenos">117</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">" content type: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">third_item</span><span class="p">.</span><span class="n">type</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">118</span><span class="w"> </span><span class="c1">// We get a scalar -- the location of 2223 in column A, which is 2 in 0-based indexing.</span> |
| <span class="linenos">119</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">third_item</span><span class="p">.</span><span class="n">scalar_as</span><span class="o"><</span><span class="n">arrow</span><span class="o">::</span><span class="n">Int64Scalar</span><span class="o">></span><span class="p">().</span><span class="n">value</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">120</span><span class="w"> </span><span class="c1">// (Doc section: Index Inspection)</span> |
| <span class="linenos">121</span><span class="w"> </span><span class="c1">// (Doc section: Ret)</span> |
| <span class="linenos">122</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">123</span><span class="p">}</span> |
| <span class="linenos">124</span><span class="c1">// (Doc section: Ret)</span> |
| <span class="linenos">125</span> |
| <span class="linenos">126</span><span class="c1">// (Doc section: Main)</span> |
| <span class="linenos">127</span><span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span><span class="w"> </span><span class="p">{</span> |
| <span class="linenos">128</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">st</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">RunMain</span><span class="p">();</span> |
| <span class="linenos">129</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">st</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">130</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">st</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">131</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span> |
| <span class="linenos">132</span><span class="w"> </span><span class="p">}</span> |
| <span class="linenos">133</span><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span> |
| <span class="linenos">134</span><span class="p">}</span> |
| <span class="linenos">135</span><span class="c1">// (Doc section: Main)</span> |
| </pre></div> |
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