com.google.cloud.dataflow.sdk.transforms

Class ApproximateUnique.ApproximateUniqueCombineFn<T>

java.lang.Object

com.google.cloud.dataflow.sdk.transforms.Combine.CombineFn<T,ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique,Long>

com.google.cloud.dataflow.sdk.transforms.ApproximateUnique.ApproximateUniqueCombineFn<T>

Type Parameters:

T - the type of the values being combined

All Implemented Interfaces:

Serializable

Enclosing class:

ApproximateUnique

public static class ApproximateUnique.ApproximateUniqueCombineFn<T>
extends Combine.CombineFn<T,ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique,Long>

CombineFn that computes an estimate of the number of distinct values that were combined.

Hashes input elements, computes the top sampleSize hash values, and uses those to extrapolate the size of the entire set of hash values by assuming the rest of the hash values are as densely distributed as the top sampleSize.

Used to implement ApproximatUnique.globally(...) and ApproximatUnique.perKey(...).

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique A heap utility class to efficiently track the largest added elements.

Constructor Summary

Constructors

Constructor and Description
ApproximateUniqueCombineFn(long sampleSize, Coder<T> coder)

Method Summary

Modifier and Type	Method and Description
ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique	addInput(ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique heap, T input) Adds the given input value to the given accumulator, returning the new accumulator value.
ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique	createAccumulator() Returns a new, mutable accumulator value, representing the accumulation of zero input values.
Long	extractOutput(ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique heap) Returns the output value that is the result of combining all the input values represented by the given accumulator.
Coder<ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique>	getAccumulatorCoder(CoderRegistry registry, Coder<T> inputCoder) Returns the Coder to use for accumulator AccumT values, or null if it is not able to be inferred.
ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique	mergeAccumulators(Iterable<ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique> heaps) 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, getDefaultOutputCoder, getOutputType

Methods inherited from class java.lang.Object

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

Constructor Detail

ApproximateUniqueCombineFn

public ApproximateUniqueCombineFn(long sampleSize,
                                  Coder<T> coder)

Method Detail

createAccumulator

public ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique createAccumulator()

Description copied from class: Combine.CombineFn

Returns a new, mutable accumulator value, representing the accumulation of zero input values.

Specified by:

createAccumulator in class Combine.CombineFn<T,ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique,Long>

addInput

public ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique addInput(ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique heap,
                                                                           T 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<T,ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique,Long>

mergeAccumulators

public ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique mergeAccumulators(Iterable<ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique> heaps)

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<T,ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique,Long>

extractOutput

public Long extractOutput(ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique heap)

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<T,ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique,Long>

getAccumulatorCoder

public Coder<ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique> getAccumulatorCoder(CoderRegistry registry,
                                                                                             Coder<T> inputCoder)

Description copied from class: Combine.CombineFn

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.

Overrides:

getAccumulatorCoder in class Combine.CombineFn<T,ApproximateUnique.ApproximateUniqueCombineFn.LargestUnique,Long>