org.apache.beam.sdk.transforms

Class Combine.AccumulatingCombineFn<InputT,AccumT extends Combine.AccumulatingCombineFn.Accumulator<InputT,AccumT,OutputT>,OutputT>

java.lang.Object

org.apache.beam.sdk.transforms.Combine.CombineFn<InputT,AccumT,OutputT>

org.apache.beam.sdk.transforms.Combine.AccumulatingCombineFn<InputT,AccumT,OutputT>

Type Parameters:

InputT - type of input values

AccumT - type of mutable accumulator values

OutputT - type of output values

All Implemented Interfaces:

java.io.Serializable, CombineFnBase.GlobalCombineFn<InputT,AccumT,OutputT>, HasDisplayData

Direct Known Subclasses:

ApproximateQuantiles.ApproximateQuantilesCombineFn, Top.TopCombineFn

Enclosing class:

Combine

public abstract static class Combine.AccumulatingCombineFn<InputT,AccumT extends Combine.AccumulatingCombineFn.Accumulator<InputT,AccumT,OutputT>,OutputT>
extends Combine.CombineFn<InputT,AccumT,OutputT>

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<InputT,AccumT,OutputT> The type of mutable accumulator values used by this AccumulatingCombineFn.

Constructor Summary

Constructors

Constructor and Description
AccumulatingCombineFn()

Method Summary

Modifier and Type	Method and Description
AccumT	addInput(AccumT accumulator, InputT input) Adds the given input value to the given accumulator, returning the new accumulator value.
OutputT	extractOutput(AccumT accumulator) Returns the output value that is the result of combining all the input values represented by the given accumulator.
java.lang.reflect.TypeVariable<?>	getAccumTVariable() Returns the TypeVariable of AccumT.
Coder<AccumT>	getAccumulatorCoder(CoderRegistry registry, Coder<InputT> inputCoder) Returns the Coder to use for accumulator AccumT values, or null if it is not able to be inferred.
Coder<OutputT>	getDefaultOutputCoder(CoderRegistry registry, Coder<InputT> inputCoder) Returns the Coder to use by default for output OutputT values, or null if it is not able to be inferred.
java.lang.String	getIncompatibleGlobalWindowErrorMessage() Returns the error message for not supported default values in Combine.globally().
java.lang.reflect.TypeVariable<?>	getInputTVariable() Returns the TypeVariable of InputT.
java.lang.reflect.TypeVariable<?>	getOutputTVariable() Returns the TypeVariable of OutputT.
AccumT	mergeAccumulators(java.lang.Iterable<AccumT> accumulators) Returns an accumulator representing the accumulation of all the input values accumulated in the merging accumulators.
void	populateDisplayData(DisplayData.Builder builder) Register display data for the given transform or component.

Methods inherited from class org.apache.beam.sdk.transforms.Combine.CombineFn

apply, compact, createAccumulator, defaultValue, getOutputType

Methods inherited from class java.lang.Object

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

Constructor Detail

AccumulatingCombineFn

public AccumulatingCombineFn()

Method Detail

addInput

public final AccumT addInput(AccumT accumulator,
                             InputT 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<InputT,AccumT extends Combine.AccumulatingCombineFn.Accumulator<InputT,AccumT,OutputT>,OutputT>

mergeAccumulators

public final AccumT mergeAccumulators(java.lang.Iterable<AccumT> 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<InputT,AccumT extends Combine.AccumulatingCombineFn.Accumulator<InputT,AccumT,OutputT>,OutputT>

extractOutput

public final OutputT extractOutput(AccumT 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<InputT,AccumT extends Combine.AccumulatingCombineFn.Accumulator<InputT,AccumT,OutputT>,OutputT>

getAccumulatorCoder

public Coder<AccumT> getAccumulatorCoder(CoderRegistry registry,
                                         Coder<InputT> inputCoder)
                                  throws CannotProvideCoderException

Description copied from interface: CombineFnBase.GlobalCombineFn

Returns the Coder to use for accumulator AccumT values, or null if it is not able to be inferred.

By default, uses the knowledge of the Coder being used for InputT values and the enclosing Pipeline's CoderRegistry to try to infer the Coder for AccumT values.

This is the Coder used to send data through a communication-intensive shuffle step, so a compact and efficient representation may have significant performance benefits.

Specified by:

getAccumulatorCoder in interface CombineFnBase.GlobalCombineFn<InputT,AccumT,OutputT>

Throws:

CannotProvideCoderException

getDefaultOutputCoder

public Coder<OutputT> getDefaultOutputCoder(CoderRegistry registry,
                                            Coder<InputT> inputCoder)
                                     throws CannotProvideCoderException

Description copied from interface: CombineFnBase.GlobalCombineFn

Returns the Coder to use by default for output OutputT values, or null if it is not able to be inferred.

By default, uses the knowledge of the Coder being used for input InputT values and the enclosing Pipeline's CoderRegistry to try to infer the Coder for OutputT values.

Specified by:

getDefaultOutputCoder in interface CombineFnBase.GlobalCombineFn<InputT,AccumT,OutputT>

Throws:

CannotProvideCoderException

getIncompatibleGlobalWindowErrorMessage

public java.lang.String getIncompatibleGlobalWindowErrorMessage()

Description copied from interface: CombineFnBase.GlobalCombineFn

Returns the error message for not supported default values in Combine.globally().

Specified by:

getIncompatibleGlobalWindowErrorMessage in interface CombineFnBase.GlobalCombineFn<InputT,AccumT,OutputT>

getInputTVariable

public java.lang.reflect.TypeVariable<?> getInputTVariable()

Returns the TypeVariable of InputT.

getAccumTVariable

public java.lang.reflect.TypeVariable<?> getAccumTVariable()

Returns the TypeVariable of AccumT.

getOutputTVariable

public java.lang.reflect.TypeVariable<?> getOutputTVariable()

Returns the TypeVariable of OutputT.

populateDisplayData

public void populateDisplayData(DisplayData.Builder builder)

Register display data for the given transform or component.

populateDisplayData(DisplayData.Builder) is invoked by Pipeline runners to collect display data via DisplayData.from(HasDisplayData). Implementations may call super.populateDisplayData(builder) in order to register display data in the current namespace, but should otherwise use subcomponent.populateDisplayData(builder) to use the namespace of the subcomponent.

By default, does not register any display data. Implementors may override this method to provide their own display data.

Specified by:

populateDisplayData in interface HasDisplayData

Parameters:

builder - The builder to populate with display data.

See Also:

HasDisplayData