com.google.cloud.dataflow.sdk.transforms

Class Combine.Globally<VI,VO>

java.lang.Object

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

com.google.cloud.dataflow.sdk.transforms.Combine.Globally<VI,VO>

Type Parameters:

VI - type of input values

VO - type of output values

All Implemented Interfaces:

java.io.Serializable

Enclosing class:

Combine

public static class Combine.Globally<VI,VO>
extends PTransform<PCollection<VI>,PCollection<VO>>

Combine.Globally<VI, VO> takes a PCollection<VI> and returns a PCollection<VO> whose single element is the result of combining all the elements of the input PCollection, using a specified CombineFn. It is common for VI == VO, but not required. Common combining functions include sums, mins, maxes, and averages of numbers, conjunctions and disjunctions of booleans, statistical aggregations, etc.

Example of use:

 PCollection<Integer> pc = ...;
 PCollection<Integer> sum = pc.apply(
     Combine.globally(new Sum.SumIntegerFn()));
  

Combining can happen in parallel, with different subsets of the input PCollection being combined separately, and their intermediate results combined further, in an arbitrary tree reduction pattern, until a single result value is produced.

By default, the Coder of the output PValue<VO> is inferred from the concrete type of the CombineFn<VI, VA, VO>'s output type VO.

See also Combine.perKey(com.google.cloud.dataflow.sdk.transforms.SerializableFunction<java.lang.Iterable<V>, V>)/Combine.PerKey and Combine.groupedValues(com.google.cloud.dataflow.sdk.transforms.SerializableFunction<java.lang.Iterable<V>, V>)/Combine.GroupedValues, which are useful for combining values associated with each key in a PCollection of KVs.

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<VO>	apply(PCollection<VI> input) Applies this PTransform on the given Input, and returns its Output.
protected 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

Method Detail

apply

public PCollection<VO> apply(PCollection<VI> 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<VI>,PCollection<VO>>

getKindString

protected 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<VI>,PCollection<VO>>