Google Cloud Dataflow SDK for Java, version 1.9.1
Class Combine.AccumulatingCombineFn<InputT,AccumT extends Combine.AccumulatingCombineFn.Accumulator<InputT,AccumT,OutputT>,OutputT>
- java.lang.Object
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- com.google.cloud.dataflow.sdk.transforms.Combine.CombineFn<InputT,AccumT,OutputT>
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- com.google.cloud.dataflow.sdk.transforms.Combine.AccumulatingCombineFn<InputT,AccumT,OutputT>
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- Type Parameters:
InputT
- type of input valuesAccumT
- type of mutable accumulator valuesOutputT
- type of output values
- All Implemented Interfaces:
- CombineFnBase.GlobalCombineFn<InputT,AccumT,OutputT>, HasDisplayData, Serializable
- 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>
ACombineFn
that uses a subclass ofCombine.AccumulatingCombineFn.Accumulator
as its accumulator type. By defining the operations of theAccumulator
helper class, the operations of the enclosingCombineFn
are automatically provided. This can reduce the code required to implement aCombineFn
.For example, the example from
Combine.CombineFn
above can be expressed usingAccumulatingCombineFn
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
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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 thisAccumulatingCombineFn
.
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Constructor Summary
Constructors Constructor and Description AccumulatingCombineFn()
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Method Summary
All Methods Instance Methods Concrete Methods 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.TypeVariable<?>
getAccumTVariable()
Returns theTypeVariable
ofAccumT
.Coder<AccumT>
getAccumulatorCoder(CoderRegistry registry, Coder<InputT> inputCoder)
Returns theCoder
to use for accumulatorAccumT
values, or null if it is not able to be inferred.Coder<OutputT>
getDefaultOutputCoder(CoderRegistry registry, Coder<InputT> inputCoder)
Returns theCoder
to use by default for outputOutputT
values, or null if it is not able to be inferred.String
getIncompatibleGlobalWindowErrorMessage()
Returns the error message for not supported default values in Combine.globally().TypeVariable<?>
getInputTVariable()
Returns theTypeVariable
ofInputT
.TypeVariable<?>
getOutputTVariable()
Returns theTypeVariable
ofOutputT
.AccumT
mergeAccumulators(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 com.google.cloud.dataflow.sdk.transforms.Combine.CombineFn
apply, asKeyedFn, compact, createAccumulator, defaultValue, getOutputType
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Method Detail
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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 classCombine.CombineFn<InputT,AccumT extends Combine.AccumulatingCombineFn.Accumulator<InputT,AccumT,OutputT>,OutputT>
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mergeAccumulators
public final AccumT mergeAccumulators(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 classCombine.CombineFn<InputT,AccumT extends Combine.AccumulatingCombineFn.Accumulator<InputT,AccumT,OutputT>,OutputT>
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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 classCombine.CombineFn<InputT,AccumT extends Combine.AccumulatingCombineFn.Accumulator<InputT,AccumT,OutputT>,OutputT>
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getAccumulatorCoder
public Coder<AccumT> getAccumulatorCoder(CoderRegistry registry, Coder<InputT> inputCoder) throws CannotProvideCoderException
Description copied from interface:CombineFnBase.GlobalCombineFn
Returns theCoder
to use for accumulatorAccumT
values, or null if it is not able to be inferred.By default, uses the knowledge of the
Coder
being used forInputT
values and the enclosingPipeline
'sCoderRegistry
to try to infer the Coder forAccumT
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 interfaceCombineFnBase.GlobalCombineFn<InputT,AccumT,OutputT>
- Throws:
CannotProvideCoderException
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getDefaultOutputCoder
public Coder<OutputT> getDefaultOutputCoder(CoderRegistry registry, Coder<InputT> inputCoder) throws CannotProvideCoderException
Description copied from interface:CombineFnBase.GlobalCombineFn
Returns theCoder
to use by default for outputOutputT
values, or null if it is not able to be inferred.By default, uses the knowledge of the
Coder
being used for inputInputT
values and the enclosingPipeline
'sCoderRegistry
to try to infer the Coder forOutputT
values.- Specified by:
getDefaultOutputCoder
in interfaceCombineFnBase.GlobalCombineFn<InputT,AccumT,OutputT>
- Throws:
CannotProvideCoderException
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getIncompatibleGlobalWindowErrorMessage
public String getIncompatibleGlobalWindowErrorMessage()
Description copied from interface:CombineFnBase.GlobalCombineFn
Returns the error message for not supported default values in Combine.globally().- Specified by:
getIncompatibleGlobalWindowErrorMessage
in interfaceCombineFnBase.GlobalCombineFn<InputT,AccumT,OutputT>
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getInputTVariable
public TypeVariable<?> getInputTVariable()
Returns theTypeVariable
ofInputT
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getAccumTVariable
public TypeVariable<?> getAccumTVariable()
Returns theTypeVariable
ofAccumT
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getOutputTVariable
public TypeVariable<?> getOutputTVariable()
Returns theTypeVariable
ofOutputT
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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 viaDisplayData.from(HasDisplayData)
. Implementations may callsuper.populateDisplayData(builder)
in order to register display data in the current namespace, but should otherwise usesubcomponent.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 interfaceHasDisplayData
- Parameters:
builder
- The builder to populate with display data.- See Also:
HasDisplayData
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