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<div class="subTitle">org.apache.beam.sdk.transforms</div>
<h2 title="Class Count" class="title">Class Count</h2>
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<pre>public class <span class="typeNameLabel">Count</span>
extends java.lang.Object</pre>
<div class="block"><a href="../../../../../org/apache/beam/sdk/transforms/PTransform.html" title="class in org.apache.beam.sdk.transforms"><code>PTransforms</code></a> to count the elements in a <a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values"><code>PCollection</code></a>.
<p><a href="../../../../../org/apache/beam/sdk/transforms/Count.html#perElement--"><code>perElement()</code></a> can be used to count the number of occurrences of each distinct
element in the PCollection, <a href="../../../../../org/apache/beam/sdk/transforms/Count.html#perKey--"><code>perKey()</code></a> can be used to count the number of values per
key, and <a href="../../../../../org/apache/beam/sdk/transforms/Count.html#globally--"><code>globally()</code></a> can be used to count the total number of elements in a
PCollection.
<p><a href="../../../../../org/apache/beam/sdk/transforms/Count.html#combineFn--"><code>combineFn()</code></a> can also be used manually, in combination with state and with the <a href="../../../../../org/apache/beam/sdk/transforms/Combine.html" title="class in org.apache.beam.sdk.transforms"><code>Combine</code></a> transform.</div>
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<h3>Method Summary</h3>
<table class="memberSummary" border="0" cellpadding="3" cellspacing="0" summary="Method Summary table, listing methods, and an explanation">
<caption><span id="t0" class="activeTableTab"><span>All Methods</span><span class="tabEnd">&nbsp;</span></span><span id="t1" class="tableTab"><span><a href="javascript:show(1);">Static Methods</a></span><span class="tabEnd">&nbsp;</span></span><span id="t4" class="tableTab"><span><a href="javascript:show(8);">Concrete Methods</a></span><span class="tabEnd">&nbsp;</span></span></caption>
<tr>
<th class="colFirst" scope="col">Modifier and Type</th>
<th class="colLast" scope="col">Method and Description</th>
</tr>
<tr id="i0" class="altColor">
<td class="colFirst"><code>static &lt;T&gt;&nbsp;<a href="../../../../../org/apache/beam/sdk/transforms/Combine.CombineFn.html" title="class in org.apache.beam.sdk.transforms">Combine.CombineFn</a>&lt;T,?,java.lang.Long&gt;</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/beam/sdk/transforms/Count.html#combineFn--">combineFn</a></span>()</code>
<div class="block">Returns a <a href="../../../../../org/apache/beam/sdk/transforms/Combine.CombineFn.html" title="class in org.apache.beam.sdk.transforms"><code>Combine.CombineFn</code></a> that counts the number of its inputs.</div>
</td>
</tr>
<tr id="i1" class="rowColor">
<td class="colFirst"><code>static &lt;T&gt;&nbsp;<a href="../../../../../org/apache/beam/sdk/transforms/PTransform.html" title="class in org.apache.beam.sdk.transforms">PTransform</a>&lt;<a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values">PCollection</a>&lt;T&gt;,<a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values">PCollection</a>&lt;java.lang.Long&gt;&gt;</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/beam/sdk/transforms/Count.html#globally--">globally</a></span>()</code>
<div class="block">Returns a <a href="../../../../../org/apache/beam/sdk/transforms/PTransform.html" title="class in org.apache.beam.sdk.transforms"><code>PTransform</code></a> that counts the number of elements in its input <a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values"><code>PCollection</code></a>.</div>
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<tr id="i2" class="altColor">
<td class="colFirst"><code>static &lt;T&gt;&nbsp;<a href="../../../../../org/apache/beam/sdk/transforms/PTransform.html" title="class in org.apache.beam.sdk.transforms">PTransform</a>&lt;<a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values">PCollection</a>&lt;T&gt;,<a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values">PCollection</a>&lt;<a href="../../../../../org/apache/beam/sdk/values/KV.html" title="class in org.apache.beam.sdk.values">KV</a>&lt;T,java.lang.Long&gt;&gt;&gt;</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/beam/sdk/transforms/Count.html#perElement--">perElement</a></span>()</code>
<div class="block">Returns a <a href="../../../../../org/apache/beam/sdk/transforms/PTransform.html" title="class in org.apache.beam.sdk.transforms"><code>PTransform</code></a> that counts the number of occurrences of each element in its input
<a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values"><code>PCollection</code></a>.</div>
</td>
</tr>
<tr id="i3" class="rowColor">
<td class="colFirst"><code>static &lt;K,V&gt;&nbsp;<a href="../../../../../org/apache/beam/sdk/transforms/PTransform.html" title="class in org.apache.beam.sdk.transforms">PTransform</a>&lt;<a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values">PCollection</a>&lt;<a href="../../../../../org/apache/beam/sdk/values/KV.html" title="class in org.apache.beam.sdk.values">KV</a>&lt;K,V&gt;&gt;,<a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values">PCollection</a>&lt;<a href="../../../../../org/apache/beam/sdk/values/KV.html" title="class in org.apache.beam.sdk.values">KV</a>&lt;K,java.lang.Long&gt;&gt;&gt;</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../../org/apache/beam/sdk/transforms/Count.html#perKey--">perKey</a></span>()</code>
<div class="block">Returns a <a href="../../../../../org/apache/beam/sdk/transforms/PTransform.html" title="class in org.apache.beam.sdk.transforms"><code>PTransform</code></a> that counts the number of elements associated with each key of its
input <a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values"><code>PCollection</code></a>.</div>
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<h3>Methods inherited from class&nbsp;java.lang.Object</h3>
<code>clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait</code></li>
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<h4>combineFn</h4>
<pre>public static&nbsp;&lt;T&gt;&nbsp;<a href="../../../../../org/apache/beam/sdk/transforms/Combine.CombineFn.html" title="class in org.apache.beam.sdk.transforms">Combine.CombineFn</a>&lt;T,?,java.lang.Long&gt;&nbsp;combineFn()</pre>
<div class="block">Returns a <a href="../../../../../org/apache/beam/sdk/transforms/Combine.CombineFn.html" title="class in org.apache.beam.sdk.transforms"><code>Combine.CombineFn</code></a> that counts the number of its inputs.</div>
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<pre>public static&nbsp;&lt;T&gt;&nbsp;<a href="../../../../../org/apache/beam/sdk/transforms/PTransform.html" title="class in org.apache.beam.sdk.transforms">PTransform</a>&lt;<a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values">PCollection</a>&lt;T&gt;,<a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values">PCollection</a>&lt;java.lang.Long&gt;&gt;&nbsp;globally()</pre>
<div class="block">Returns a <a href="../../../../../org/apache/beam/sdk/transforms/PTransform.html" title="class in org.apache.beam.sdk.transforms"><code>PTransform</code></a> that counts the number of elements in its input <a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values"><code>PCollection</code></a>.
<p>Note: if the input collection uses a windowing strategy other than <a href="../../../../../org/apache/beam/sdk/transforms/windowing/GlobalWindows.html" title="class in org.apache.beam.sdk.transforms.windowing"><code>GlobalWindows</code></a>,
use <code>Combine.globally(Count.&lt;T&gt;combineFn()).withoutDefaults()</code> instead.</div>
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<pre>public static&nbsp;&lt;K,V&gt;&nbsp;<a href="../../../../../org/apache/beam/sdk/transforms/PTransform.html" title="class in org.apache.beam.sdk.transforms">PTransform</a>&lt;<a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values">PCollection</a>&lt;<a href="../../../../../org/apache/beam/sdk/values/KV.html" title="class in org.apache.beam.sdk.values">KV</a>&lt;K,V&gt;&gt;,<a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values">PCollection</a>&lt;<a href="../../../../../org/apache/beam/sdk/values/KV.html" title="class in org.apache.beam.sdk.values">KV</a>&lt;K,java.lang.Long&gt;&gt;&gt;&nbsp;perKey()</pre>
<div class="block">Returns a <a href="../../../../../org/apache/beam/sdk/transforms/PTransform.html" title="class in org.apache.beam.sdk.transforms"><code>PTransform</code></a> that counts the number of elements associated with each key of its
input <a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values"><code>PCollection</code></a>.</div>
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<pre>public static&nbsp;&lt;T&gt;&nbsp;<a href="../../../../../org/apache/beam/sdk/transforms/PTransform.html" title="class in org.apache.beam.sdk.transforms">PTransform</a>&lt;<a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values">PCollection</a>&lt;T&gt;,<a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values">PCollection</a>&lt;<a href="../../../../../org/apache/beam/sdk/values/KV.html" title="class in org.apache.beam.sdk.values">KV</a>&lt;T,java.lang.Long&gt;&gt;&gt;&nbsp;perElement()</pre>
<div class="block">Returns a <a href="../../../../../org/apache/beam/sdk/transforms/PTransform.html" title="class in org.apache.beam.sdk.transforms"><code>PTransform</code></a> that counts the number of occurrences of each element in its input
<a href="../../../../../org/apache/beam/sdk/values/PCollection.html" title="class in org.apache.beam.sdk.values"><code>PCollection</code></a>.
<p>The returned <code>PTransform</code> takes a <code>PCollection&lt;T&gt;</code> and returns a <code>PCollection&lt;KV&lt;T, Long&gt;&gt;</code> representing a map from each distinct element of the input <code>PCollection</code> to the number of times that element occurs in the input. Each key in the output
<code>PCollection</code> is unique.
<p>The returned transform compares two values of type <code>T</code> by first encoding each element
using the input <code>PCollection</code>'s <code>Coder</code>, then comparing the encoded bytes. Because
of this, the input coder must be deterministic. (See <a href="../../../../../org/apache/beam/sdk/coders/Coder.html#verifyDeterministic--"><code>Coder.verifyDeterministic()</code></a> for more detail). Performing the
comparison in this manner admits efficient parallel evaluation.
<p>By default, the <code>Coder</code> of the keys of the output <code>PCollection</code> is the same as
the <code>Coder</code> of the elements of the input <code>PCollection</code>.
<p>Example of use:
<pre><code>
PCollection&lt;String&gt; words = ...;
PCollection&lt;KV&lt;String, Long&gt;&gt; wordCounts =
words.apply(Count.&lt;String&gt;perElement());
</code></pre></div>
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