com.google.cloud.dataflow.sdk.transforms

Class Keys<K>

java.lang.Object

com.google.cloud.dataflow.sdk.transforms.PTransform<PCollection<? extends KV<K,?>>,PCollection<K>>

com.google.cloud.dataflow.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:

HasDisplayData, Serializable

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 com.google.cloud.dataflow.sdk.transforms.PTransform

name

Method Summary

Modifier and Type	Method and Description
PCollection<K>	apply(PCollection<? extends KV<K,?>> in) Applies this PTransform on the given InputT, and returns its Output.
static <K> Keys<K>	create() Returns a Keys<K> PTransform.

Methods inherited from class com.google.cloud.dataflow.sdk.transforms.PTransform

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

apply

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

Description copied from class: PTransform

Applies this PTransform on the given InputT, and returns its Output.

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).

The default implementation throws an exception. A derived class must either implement apply, or else each runner must supply a custom implementation via PipelineRunner.apply(com.google.cloud.dataflow.sdk.transforms.PTransform<InputT, OutputT>, InputT).

Overrides:

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