com.google.cloud.dataflow.sdk.transforms

Class Combine.AccumulatingCombineFn<VI,VA extends Combine.AccumulatingCombineFn.Accumulator<VI,VA,VO>,VO>

java.lang.Object

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

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

Type Parameters:

VI - type of input values

VA - type of mutable accumulator values

VO - type of output values

All Implemented Interfaces:

java.io.Serializable

Direct Known Subclasses:

ApproximateQuantiles.ApproximateQuantilesCombineFn, Mean.MeanFn, Top.TopCombineFn

Enclosing class:

Combine

public abstract static class Combine.AccumulatingCombineFn<VI,VA extends Combine.AccumulatingCombineFn.Accumulator<VI,VA,VO>,VO>
extends Combine.CombineFn<VI,VA,VO>

A CombineFn that uses a subclass of Combine.AccumulatingCombineFn.Accumulator as its accumulator type. By defining the operations of the Accumulator helper class, the operations of the enclosing CombineFn are automatically provided. This can reduce the code required to implement a CombineFn.

For example, the example from Combine.CombineFn above can be expressed using AccumulatingCombineFn more concisely as follows:

 public class AverageFn
     extends AccumulatingCombineFn<Integer, AverageFn.Accum, Double> {
   public Accum createAccumulator() { return new Accum(); }
   public class Accum
       extends AccumulatingCombineFn<Integer, AverageFn.Accum, Double>
               .Accumulator {
     private int sum = 0;
     private int count = 0;
     public void addInput(Integer input) {
       sum += input;
       count++;
     }
     public void mergeAccumulator(Accum other) {
       sum += other.sum;
       count += other.count;
     }
     public Double extractOutput() {
       return ((double) sum) / count;
     }
   }
 }
 PCollection<Integer> pc = ...;
 PCollection<Double> average = pc.apply(Combine.globally(new AverageFn()));
  

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	Combine.AccumulatingCombineFn.Accumulator<VI,VA,VO> The type of mutable accumulator values used by this AccumulatingCombineFn.

Constructor Summary

Constructors

Constructor and Description
Combine.AccumulatingCombineFn()

Method Summary

Methods

Modifier and Type	Method and Description
VA	addInput(VA accumulator, VI input) Adds the given input value to the given accumulator, returning the new accumulator value.
VO	extractOutput(VA accumulator) Returns the output value that is the result of combining all the input values represented by the given accumulator.
VA	mergeAccumulators(java.lang.Iterable<VA> accumulators) Returns an accumulator representing the accumulation of all the input values accumulated in the merging accumulators.

Methods inherited from class com.google.cloud.dataflow.sdk.transforms.Combine.CombineFn

apply, asKeyedFn, createAccumulator, getAccumulatorCoder, getDefaultOutputCoder

Methods inherited from class java.lang.Object

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

Constructor Detail

Combine.AccumulatingCombineFn

public Combine.AccumulatingCombineFn()

Method Detail

addInput

public final VA addInput(VA accumulator,
          VI input)

Description copied from class: Combine.CombineFn

Adds the given input value to the given accumulator, returning the new accumulator value.

For efficiency, the input accumulator may be modified and returned.

Specified by:

addInput in class Combine.CombineFn<VI,VA extends Combine.AccumulatingCombineFn.Accumulator<VI,VA,VO>,VO>

mergeAccumulators

public final VA mergeAccumulators(java.lang.Iterable<VA> accumulators)

Description copied from class: Combine.CombineFn

Returns an accumulator representing the accumulation of all the input values accumulated in the merging accumulators.

May modify any of the argument accumulators. May return a fresh accumulator, or may return one of the (modified) argument accumulators.

Specified by:

mergeAccumulators in class Combine.CombineFn<VI,VA extends Combine.AccumulatingCombineFn.Accumulator<VI,VA,VO>,VO>

extractOutput

public final VO extractOutput(VA accumulator)

Description copied from class: Combine.CombineFn

Returns the output value that is the result of combining all the input values represented by the given accumulator.

Specified by:

extractOutput in class Combine.CombineFn<VI,VA extends Combine.AccumulatingCombineFn.Accumulator<VI,VA,VO>,VO>