# Apache Beam: Keys

## Overview

What if you only care about the keys of your PCollection and not necessarily the values? Maybe you have KV pairs for words and their counts in a string (KV<String, Integer>) and want to use the list of words in another PCollection.

You should use the `Keys` transform!

## When You Should Use the Keys Transform

When you only want the keys in from a KV PCollection.

## How to Use the Keys Transform

Just apply the builtin Transform to a PCollection of KVs. The output PCollection will have the type of the Keys in the KV and be flattened for all input elements.

## Example: Extract Keys 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 only the values of the collection: PCollection<KV<K,V>> ->
    // PCollection<V>
    PCollection<String> valuesOnly = pairs.apply(Keys.create());
```

## Conclusion

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