com.google.cloud.dataflow.sdk.transforms

Class First<T>

java.lang.Object

com.google.cloud.dataflow.sdk.transforms.PTransform<PCollection<T>,PCollection<T>>

com.google.cloud.dataflow.sdk.transforms.First<T>

Type Parameters:

T - the type of the elements of the input and output PCollections

All Implemented Interfaces:

java.io.Serializable

public class First<T>
extends PTransform<PCollection<T>,PCollection<T>>

First<T> takes a PCollection<T> and a limit, and produces a new PCollection<T> containing up to limit elements of the input PCollection.

If the input and output PCollections are ordered, then First will select the first elements, otherwise it will select any elements.

If limit is less than or equal to the size of the input PCollection, then all the input's elements will be selected.

All of the elements of the output PCollection should fit into main memory of a single worker machine. This operation does not run in parallel.

Example of use:

 PCollection<String> input = ...;
 PCollection<String> output = input.apply(First.<String>of(100));
  

See Also:

Serialized Form

Field Summary

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

name

Method Summary

Methods

Modifier and Type	Method and Description
PCollection<T>	apply(PCollection<T> in) Applies this PTransform on the given Input, and returns its Output.
static <T> First<T>	of(long limit) Returns a First<T> PTransform.

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

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

Methods inherited from class java.lang.Object

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

Method Detail

of

public static <T> First<T> of(long limit)

Returns a First<T> PTransform.

Type Parameters:

T - the type of the elements of the input and output PCollections

Parameters:

limit - the numer of elements to take from the input

apply

public PCollection<T> apply(PCollection<T> in)

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<T>>