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href=/documentation/transforms/python/elementwise/regex/>Regex</a></li><li><a href=/documentation/transforms/python/elementwise/reify/>Reify</a></li><li class=section-nav-item--collapsible><span class=section-nav-list-title>RunInference</span><ul class=section-nav-list><li><a href=/documentation/transforms/python/elementwise/runinference/>Overview</a></li><li><a href=/documentation/transforms/python/elementwise/runinference-pytorch/>PyTorch examples</a></li><li><a href=/documentation/transforms/python/elementwise/runinference-sklearn/>Sklearn examples</a></li></ul></li><li><a href=/documentation/transforms/python/elementwise/tostring/>ToString</a></li><li><a href=/documentation/transforms/python/elementwise/values/>Values</a></li><li><a href=/documentation/transforms/python/elementwise/withtimestamps/>WithTimestamps</a></li></ul></li><li class=section-nav-item--collapsible><span class=section-nav-list-title>Aggregation</span><ul class=section-nav-list><li><a href=/documentation/transforms/python/aggregation/approximatequantiles/>ApproximateQuantiles</a></li><li><a href=/documentation/transforms/python/aggregation/approximateunique/>ApproximateUnique</a></li><li><a href=/documentation/transforms/python/aggregation/cogroupbykey/>CoGroupByKey</a></li><li><a href=/documentation/transforms/python/aggregation/combineglobally/>CombineGlobally</a></li><li><a href=/documentation/transforms/python/aggregation/combineperkey/>CombinePerKey</a></li><li><a href=/documentation/transforms/python/aggregation/combinevalues/>CombineValues</a></li><li><a href=/documentation/transforms/python/aggregation/count/>Count</a></li><li><a href=/documentation/transforms/python/aggregation/distinct/>Distinct</a></li><li><a href=/documentation/transforms/python/aggregation/groupby/>GroupBy</a></li><li><a href=/documentation/transforms/python/aggregation/groupbykey/>GroupByKey</a></li><li><a href=/documentation/transforms/python/aggregation/groupintobatches/>GroupIntoBatches</a></li><li><a href=/documentation/transforms/python/aggregation/latest/>Latest</a></li><li><a href=/documentation/transforms/python/aggregation/max/>Max</a></li><li><a href=/documentation/transforms/python/aggregation/mean/>Mean</a></li><li><a href=/documentation/transforms/python/aggregation/min/>Min</a></li><li><a href=/documentation/transforms/python/aggregation/sample/>Sample</a></li><li><a href=/documentation/transforms/python/aggregation/sum/>Sum</a></li><li><a href=/documentation/transforms/python/aggregation/top/>Top</a></li><li><a href=/documentation/transforms/python/aggregation/tolist/>ToList</a></li></ul></li><li class=section-nav-item--collapsible><span class=section-nav-list-title>Other</span><ul class=section-nav-list><li><a href=/documentation/transforms/python/other/create/>Create</a></li><li><a href=/documentation/transforms/python/other/flatten/>Flatten</a></li><li><a href=/documentation/transforms/python/other/reshuffle/>Reshuffle</a></li><li><a href=/documentation/transforms/python/other/windowinto/>WindowInto</a></li></ul></li></ul></li><li class=section-nav-item--collapsible><span class=section-nav-list-title>Java</span><ul class=section-nav-list><li><a href=/documentation/transforms/java/overview/>Overview</a></li><li class=section-nav-item--collapsible><span class=section-nav-list-title>Element-wise</span><ul class=section-nav-list><li><a href=/documentation/transforms/java/elementwise/filter/>Filter</a></li><li><a href=/documentation/transforms/java/elementwise/flatmapelements/>FlatMapElements</a></li><li><a href=/documentation/transforms/java/elementwise/keys/>Keys</a></li><li><a href=/documentation/transforms/java/elementwise/kvswap/>KvSwap</a></li><li><a href=/documentation/transforms/java/elementwise/mapelements/>MapElements</a></li><li><a href=/documentation/transforms/java/elementwise/pardo/>ParDo</a></li><li><a href=/documentation/transforms/java/elementwise/partition/>Partition</a></li><li><a href=/documentation/transforms/java/elementwise/regex/>Regex</a></li><li><a href=/documentation/transforms/java/elementwise/reify/>Reify</a></li><li><a href=/documentation/transforms/java/elementwise/tostring/>ToString</a></li><li><a href=/documentation/transforms/java/elementwise/values/>Values</a></li><li><a href=/documentation/transforms/java/elementwise/withkeys/>WithKeys</a></li><li><a href=/documentation/transforms/java/elementwise/withtimestamps/>WithTimestamps</a></li></ul></li><li class=section-nav-item--collapsible><span class=section-nav-list-title>Aggregation</span><ul class=section-nav-list><li><a href=/documentation/transforms/java/aggregation/approximatequantiles/>ApproximateQuantiles</a></li><li><a href=/documentation/transforms/java/aggregation/approximateunique/>ApproximateUnique</a></li><li><a href=/documentation/transforms/java/aggregation/cogroupbykey/>CoGroupByKey</a></li><li><a href=/documentation/transforms/java/aggregation/combine/>Combine</a></li><li><a href=/documentation/transforms/java/aggregation/combinewithcontext/>CombineWithContext</a></li><li><a href=/documentation/transforms/java/aggregation/count/>Count</a></li><li><a href=/documentation/transforms/java/aggregation/distinct/>Distinct</a></li><li><a href=/documentation/transforms/java/aggregation/groupbykey/>GroupByKey</a></li><li><a href=/documentation/transforms/java/aggregation/groupintobatches/>GroupIntoBatches</a></li><li><a href=/documentation/transforms/java/aggregation/hllcount/>HllCount</a></li><li><a href=/documentation/transforms/java/aggregation/latest/>Latest</a></li><li><a href=/documentation/transforms/java/aggregation/max/>Max</a></li><li><a href=/documentation/transforms/java/aggregation/mean/>Mean</a></li><li><a href=/documentation/transforms/java/aggregation/min/>Min</a></li><li><a href=/documentation/transforms/java/aggregation/sample/>Sample</a></li><li><a href=/documentation/transforms/java/aggregation/sum/>Sum</a></li><li><a href=/documentation/transforms/java/aggregation/top/>Top</a></li></ul></li><li class=section-nav-item--collapsible><span class=section-nav-list-title>Other</span><ul class=section-nav-list><li><a href=/documentation/transforms/java/other/create/>Create</a></li><li><a href=/documentation/transforms/java/other/flatten/>Flatten</a></li><li><a href=/documentation/transforms/java/other/passert/>PAssert</a></li><li><a href=/documentation/transforms/java/other/view/>View</a></li><li><a href=/documentation/transforms/java/other/window/>Window</a></li></ul></li></ul></li></ul></li><li><a href=/documentation/glossary/>Glossary</a></li><li><a href=https://cwiki.apache.org/confluence/display/BEAM/Apache+Beam>Beam Wiki <img src=/images/external-link-icon.png width=14 height=14 alt="External link."></a></li></ul></nav></div><nav class="page-nav clearfix" data-offset-top=90 data-offset-bottom=500><nav id=TableOfContents><ul><li><a href=#examples>Examples</a><ul><li><a href=#example-1-partition-with-a-function>Example 1: Partition with a function</a></li><li><a href=#example-2-partition-with-a-lambda-function>Example 2: Partition with a lambda function</a></li><li><a href=#example-3-partition-with-multiple-arguments>Example 3: Partition with multiple arguments</a></li></ul></li><li><a href=#related-transforms>Related transforms</a></li></ul></nav></nav><div class="body__contained body__section-nav arrow-list arrow-list--no-mt"><h1 id=partition>Partition</h1><script type=text/javascript>localStorage.setItem("language","language-py")</script><table align=left style=margin-right:1em><td><a class=button target=_blank href=https://beam.apache.org/releases/pydoc/current/apache_beam.transforms.core.html#apache_beam.transforms.core.Partition><img src=https://beam.apache.org/images/logos/sdks/python.png width=32px height=32px alt=Pydoc>
Pydoc</a></td></table><p><br><br><br></p><p>Separates elements in a collection into multiple output
collections. The partitioning function contains the logic that determines how
to separate the elements of the input collection into each resulting
partition output collection.</p><p>The number of partitions must be determined at graph construction time.
You cannot determine the number of partitions in mid-pipeline</p><p>See more information in the <a href=/documentation/programming-guide/#partition>Beam Programming Guide</a>.</p><h2 id=examples>Examples</h2><p>In the following examples, we create a pipeline with a <code>PCollection</code> of produce with their icon, name, and duration.
Then, we apply <code>Partition</code> in multiple ways to split the <code>PCollection</code> into multiple <code>PCollections</code>.</p><p><code>Partition</code> accepts a function that receives the number of partitions,
and returns the index of the desired partition for the element.
The number of partitions passed must be a positive integer,
and it must return an integer in the range <code>0</code> to <code>num_partitions-1</code>.</p><h3 id=example-1-partition-with-a-function>Example 1: Partition with a function</h3><p>In the following example, we have a known list of durations.
We partition the <code>PCollection</code> into one <code>PCollection</code> for every duration type.</p><div class=playground-wrapper><div class=playground-snippets><div class="language-py playground-snippet" data-sdk=python data-path=SDK_PYTHON_PartitionFunction data-show=partition_function></div></div><div class="code-snippet code-snippet-playground" data-src="https://play.beam.apache.org/embedded?editable=1&examples=%5b%7b%22path%22%3a%22SDK_PYTHON_PartitionFunction%22%2c%22sdk%22%3a%22python%22%2c%22show%22%3a%22partition_function%22%7d%5d" data-width=100% data-height=700px></div></div><h3 id=example-2-partition-with-a-lambda-function>Example 2: Partition with a lambda function</h3><p>We can also use lambda functions to simplify <strong>Example 1</strong>.</p><div class=playground-wrapper><div class=playground-snippets><div class="language-py playground-snippet" data-sdk=python data-path=SDK_PYTHON_PartitionLambda data-show=partition_lambda></div></div><div class="code-snippet code-snippet-playground" data-src="https://play.beam.apache.org/embedded?editable=1&examples=%5b%7b%22path%22%3a%22SDK_PYTHON_PartitionLambda%22%2c%22sdk%22%3a%22python%22%2c%22show%22%3a%22partition_lambda%22%7d%5d" data-width=100% data-height=700px></div></div><h3 id=example-3-partition-with-multiple-arguments>Example 3: Partition with multiple arguments</h3><p>You can pass functions with multiple arguments to <code>Partition</code>.
They are passed as additional positional arguments or keyword arguments to the function.</p><p>In machine learning, it is a common task to split data into
<a href=https://en.wikipedia.org/wiki/Training,_validation,_and_test_sets>training and a testing datasets</a>.
Typically, 80% of the data is used for training a model and 20% is used for testing.</p><p>In this example, we split a <code>PCollection</code> dataset into training and testing datasets.
We define <code>split_dataset</code>, which takes the <code>plant</code> element, <code>num_partitions</code>,
and an additional argument <code>ratio</code>.
The <code>ratio</code> is a list of numbers which represents the ratio of how many items will go into each partition.
<code>num_partitions</code> is used by <code>Partitions</code> as a positional argument,
while <code>plant</code> and <code>ratio</code> are passed to <code>split_dataset</code>.</p><p>If we want an 80%/20% split, we can specify a ratio of <code>[8, 2]</code>, which means that for every 10 elements,
8 go into the first partition and 2 go into the second.
In order to determine which partition to send each element, we have different buckets.
For our case <code>[8, 2]</code> has <strong>10</strong> buckets,
where the first 8 buckets represent the first partition and the last 2 buckets represent the second partition.</p><p>First, we check that the ratio list&rsquo;s length corresponds to the <code>num_partitions</code> we pass.
We then get a bucket index for each element, in the range from 0 to 9 (<code>num_buckets-1</code>).
We could do <code>hash(element) % len(ratio)</code>, but instead we sum all the ASCII characters of the
JSON representation to make it deterministic.
Finally, we loop through all the elements in the ratio and have a running total to
identify the partition index to which that bucket corresponds.</p><p>This <code>split_dataset</code> function is generic enough to support any number of partitions by any ratio.
You might want to adapt the bucket assignment to use a more appropriate or randomized hash for your dataset.</p><div class=playground-wrapper><div class=playground-snippets><div class="language-py playground-snippet" data-sdk=python data-path=SDK_PYTHON_PartitionMultipleArguments data-show=partition_multiple_arguments></div></div><div class="code-snippet code-snippet-playground" data-src="https://play.beam.apache.org/embedded?editable=1&examples=%5b%7b%22path%22%3a%22SDK_PYTHON_PartitionMultipleArguments%22%2c%22sdk%22%3a%22python%22%2c%22show%22%3a%22partition_multiple_arguments%22%7d%5d" data-width=100% data-height=700px></div></div><h2 id=related-transforms>Related transforms</h2><ul><li><a href=/documentation/transforms/python/elementwise/filter>Filter</a> is useful if the function is just
deciding whether to output an element or not.</li><li><a href=/documentation/transforms/python/elementwise/pardo>ParDo</a> is the most general elementwise mapping
operation, and includes other abilities such as multiple output collections and side-inputs.</li><li><a href=/documentation/transforms/python/aggregation/cogroupbykey>CoGroupByKey</a>
performs a per-key equijoin.</li></ul><table align=left style=margin-right:1em><td><a class=button target=_blank href=https://beam.apache.org/releases/pydoc/current/apache_beam.transforms.core.html#apache_beam.transforms.core.Partition><img src=https://beam.apache.org/images/logos/sdks/python.png width=32px height=32px alt=Pydoc>
Pydoc</a></td></table><p><br><br><br></p><div class=feedback><p class=update>Last updated on 2024/04/25</p><h3>Have you found everything you were looking for?</h3><p class=description>Was it all useful and clear? Is there anything that you would like to change? Let us know!</p><button class=load-button><a href="https://docs.google.com/forms/d/e/1FAIpQLSfID7abne3GE6k6RdJIyZhPz2Gef7UkpggUEhTIDjjplHuxSA/viewform?usp=header_link" target=_blank>SEND FEEDBACK</a></button></div></div></div><footer class=footer><div class=footer__contained><div class=footer__cols><div class="footer__cols__col footer__cols__col__logos"><div class=footer__cols__col__logo><img src=/images/beam_logo_circle.svg class=footer__logo alt="Beam logo"></div><div class=footer__cols__col__logo><img src=/images/apache_logo_circle.svg class=footer__logo alt="Apache logo"></div></div><div class=footer-wrapper><div class=wrapper-grid><div class=footer__cols__col><div class=footer__cols__col__title>Start</div><div class=footer__cols__col__link><a href=/get-started/beam-overview/>Overview</a></div><div class=footer__cols__col__link><a href=/get-started/quickstart-java/>Quickstart (Java)</a></div><div class=footer__cols__col__link><a href=/get-started/quickstart-py/>Quickstart (Python)</a></div><div class=footer__cols__col__link><a href=/get-started/quickstart-go/>Quickstart (Go)</a></div><div class=footer__cols__col__link><a href=/get-started/downloads/>Downloads</a></div></div><div class=footer__cols__col><div class=footer__cols__col__title>Docs</div><div class=footer__cols__col__link><a href=/documentation/programming-guide/>Concepts</a></div><div class=footer__cols__col__link><a href=/documentation/pipelines/design-your-pipeline/>Pipelines</a></div><div class=footer__cols__col__link><a href=/documentation/runners/capability-matrix/>Runners</a></div></div><div class=footer__cols__col><div class=footer__cols__col__title>Community</div><div class=footer__cols__col__link><a href=/contribute/>Contribute</a></div><div class=footer__cols__col__link><a href=https://projects.apache.org/committee.html?beam target=_blank>Team<img src=/images/external-link-icon.png width=14 height=14 alt="External link."></a></div><div class=footer__cols__col__link><a href=/community/presentation-materials/>Media</a></div><div class=footer__cols__col__link><a href=/community/in-person/>Events/Meetups</a></div><div class=footer__cols__col__link><a href=/community/contact-us/>Contact Us</a></div></div><div class=footer__cols__col><div class=footer__cols__col__title>Resources</div><div class=footer__cols__col__link><a href=/blog/>Blog</a></div><div class=footer__cols__col__link><a href=https://github.com/apache/beam>GitHub</a></div></div></div><div class=footer__bottom>&copy;
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