org.apache.beam.sdk.transforms

Class Keys<K>

java.lang.Object

org.apache.beam.sdk.transforms.PTransform<PCollection<? extends KV<K,?>>,PCollection<K>>

org.apache.beam.sdk.transforms.Keys<K>

Type Parameters:

K - the type of the keys in the input PCollection, and the type of the elements in the output PCollection

All Implemented Interfaces:

java.io.Serializable, HasDisplayData

public class Keys<K>
extends PTransform<PCollection<? extends KV<K,?>>,PCollection<K>>

Keys<K> takes a PCollection of KV<K, V>s and returns a PCollection<K> of the keys.

Example of use:

 PCollection<KV<String, Long>> wordCounts = ...;
 PCollection<String> words = wordCounts.apply(Keys.<String>create());
 

Each output element has the same timestamp and is in the same windows as its corresponding input element, and the output PCollection has the same WindowFn associated with it as the input.

See also Values.

See Also:

Serialized Form

Field Summary

Fields inherited from class org.apache.beam.sdk.transforms.PTransform

name

Method Summary

Modifier and Type	Method and Description
static <K> Keys<K>	create() Returns a Keys<K> PTransform.
PCollection<K>	expand(PCollection<? extends KV<K,?>> in) Override this method to specify how this PTransform should be expanded on the given InputT.

Methods inherited from class org.apache.beam.sdk.transforms.PTransform

compose, getAdditionalInputs, getDefaultOutputCoder, getDefaultOutputCoder, getDefaultOutputCoder, getKindString, getName, populateDisplayData, toString, validate

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Method Detail

create

public static <K> Keys<K> create()

Returns a Keys<K> PTransform.

Type Parameters:

K - the type of the keys in the input PCollection, and the type of the elements in the output PCollection

expand

public PCollection<K> expand(PCollection<? extends KV<K,?>> in)

Description copied from class: PTransform

Override this method to specify how this PTransform should be expanded on the given InputT.

NOTE: This method should not be called directly. Instead apply the PTransform should be applied to the InputT using the apply method.

Composite transforms, which are defined in terms of other transforms, should return the output of one of the composed transforms. Non-composite transforms, which do not apply any transforms internally, should return a new unbound output and register evaluators (via backend-specific registration methods).

Specified by:

expand in class PTransform<PCollection<? extends KV<K,?>>,PCollection<K>>