<h2 id="heading-overview">Overview</h2>
<p>What if you have a Key-Value pair, but want to group on the values, not the keys? Should you write a custom doFn to switch the keys and values?</p>
<p>NO!</p>
<p>You should use the <code>KvSwap</code> transform!</p>
<h2 id="heading-when-you-should-use-the-kvswap-transform">When You Should Use the KvSwap Transform</h2>
<p>When you want to easily swap the keys and values of a PCollection of KV pairs.</p>
<h2 id="heading-how-to-use-the-kvswap-transform">How to Use the KvSwap Transform</h2>
<p>Just apply the built-in Transform to a PCollection of KVs. The output PCollection will have the Keys and Values swapped from the input KV.</p>
<h2 id="heading-example-swap-keys-and-values-from-word-counts">Example: Swap Keys and Values from Word Counts</h2>
<pre><code class="lang-java">    <span class="hljs-comment">// Create key/value pairs</span>
    PCollection&lt;KV&lt;String, Integer&gt;&gt; pairs =
        pipeline.apply(
            Create.of(KV.of(<span class="hljs-string">"one"</span>, <span class="hljs-number">1</span>), KV.of(<span class="hljs-string">"two"</span>, <span class="hljs-number">2</span>), KV.of(<span class="hljs-string">"three"</span>, <span class="hljs-number">3</span>), KV.of(<span class="hljs-string">"four"</span>, <span class="hljs-number">4</span>)));
    <span class="hljs-comment">// Returns KV collection with keys and values swapped: PCollection&lt;KV&lt;K,V&gt;&gt; -&gt;</span>
    <span class="hljs-comment">// PCollection&lt;KV&lt;V,K&gt;&gt;</span>
    PCollection&lt;KV&lt;Integer, String&gt;&gt; swap = pairs.apply(KvSwap.create());
</code></pre>
<h2 id="heading-conclusion">Conclusion</h2>
<p>Check out other useful transforms from the <a target="_blank" href="https://beam.apache.org/documentation/transforms/java/overview/">official Apache Beam documentation</a>.</p>


## Overview

What if you have a Key-Value pair, but want to group on the values, not the keys? Should you write a custom doFn to switch the keys and values?

NO!

You should use the `KvSwap` transform!

## When You Should Use the KvSwap Transform

When you want to easily swap the keys and values of a PCollection of KV pairs.

## How to Use the KvSwap Transform

Just apply the built-in Transform to a PCollection of KVs. The output PCollection will have the Keys and Values swapped from the input KV.

## Example: Swap Keys and Values from Word Counts

```java
    // Create key/value pairs
    PCollection<KV<String, Integer>> pairs =
        pipeline.apply(
            Create.of(KV.of("one", 1), KV.of("two", 2), KV.of("three", 3), KV.of("four", 4)));
    // Returns KV collection with keys and values swapped: PCollection<KV<K,V>> ->
    // PCollection<KV<V,K>>
    PCollection<KV<Integer, String>> swap = pairs.apply(KvSwap.create());
    
```

## Conclusion

Check out other useful transforms from the [official Apache Beam documentation](https://beam.apache.org/documentation/transforms/java/overview/).

Swap the Keys and Values of a Key-Value Pair

Apache Beam: KvSwap

Overview

Nikhil Rao's Blog

Nikhil Rao's Blog

Apache Beam: KvSwap

Swap the Keys and Values of a Key-Value Pair

Table of contents

Overview

When You Should Use the KvSwap Transform

How to Use the KvSwap Transform

Example: Swap Keys and Values from Word Counts

Conclusion