com.google.cloud.dataflow.sdk.transforms

Class Count.PerElement<T>

java.lang.Object

com.google.cloud.dataflow.sdk.transforms.PTransform<PCollection<T>,PCollection<KV<T,java.lang.Long>>>

com.google.cloud.dataflow.sdk.transforms.Count.PerElement<T>

Type Parameters:

T - the type of the elements of the input PCollection, and the type of the keys of the output PCollection

All Implemented Interfaces:

java.io.Serializable

Enclosing class:

Count

public static class Count.PerElement<T>
extends PTransform<PCollection<T>,PCollection<KV<T,java.lang.Long>>>

Count.PerElement<T> takes a PCollection<T> and returns a PCollection<KV<T, Long>> representing a map from each distinct element of the input PCollection to the number of times that element occurs in the input. Each of the keys in the output PCollection is unique.

This transform compares two values of type T by first encoding each element using the input PCollection's Coder, then comparing the encoded bytes. Because of this, the input coder must be deterministic. (See Coder.verifyDeterministic() for more detail). Performing the comparison in this manner admits efficient parallel evaluation.

By default, the Coder of the keys of the output PCollection is the same as the Coder of the elements of the input PCollection.

Example of use:

 PCollection<String> words = ...;
 PCollection<KV<String, Long>> wordCounts =
     words.apply(Count.<String>perElement());
  

See Also:

Serialized Form

Field Summary

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

name

Constructor Summary

Constructors

Constructor and Description
Count.PerElement()

Method Summary

Methods

Modifier and Type	Method and Description
PCollection<KV<T,java.lang.Long>>	apply(PCollection<T> input) Applies this PTransform on the given Input, and returns its Output.
java.lang.String	getKindString() Returns a string describing what kind of PTransform this is.

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

finishSpecifying, getCoderRegistry, getDefaultName, getDefaultOutputCoder, getDefaultOutputCoder, getInput, getName, getOutput, getPipeline, setName, setPipeline, toString, withName

Methods inherited from class java.lang.Object

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

Constructor Detail

Count.PerElement

public Count.PerElement()

Method Detail

apply

public PCollection<KV<T,java.lang.Long>> apply(PCollection<T> input)

Description copied from class: PTransform

Applies this PTransform on the given Input, 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<Input, Output>, Input).

Overrides:

apply in class PTransform<PCollection<T>,PCollection<KV<T,java.lang.Long>>>

getKindString

public java.lang.String getKindString()

Description copied from class: PTransform

Returns a string describing what kind of PTransform this is.

By default, returns the base name of this PTransform's class.

Overrides:

getKindString in class PTransform<PCollection<T>,PCollection<KV<T,java.lang.Long>>>