org.apache.beam.sdk.transforms

Interface CombineFnBase.PerKeyCombineFn<K,InputT,AccumT,OutputT>

Type Parameters:

K - type of keys

InputT - type of input values

AccumT - type of mutable accumulator values

OutputT - type of output values

All Superinterfaces:

HasDisplayData, Serializable

All Known Implementing Classes:

Combine.KeyedCombineFn, CombineFns.ComposedKeyedCombineFn, CombineFns.ComposedKeyedCombineFnWithContext, CombineWithContext.KeyedCombineFnWithContext

Enclosing class:

CombineFnBase

public static interface CombineFnBase.PerKeyCombineFn<K,InputT,AccumT,OutputT>
extends Serializable, HasDisplayData

A PerKeyCombineFn<K, InputT, AccumT, OutputT> specifies how to combine a collection of input values of type InputT, associated with a key of type K, into a single output value of type OutputT. It does this via one or more intermediate mutable accumulator values of type AccumT.

Do not implement this interface directly. Extends Combine.KeyedCombineFn and CombineWithContext.KeyedCombineFnWithContext instead.

Method Summary

Modifier and Type	Method and Description
CombineFnBase.GlobalCombineFn<InputT,AccumT,OutputT>	forKey(K key, Coder<K> keyCoder) Returns the a regular CombineFnBase.GlobalCombineFn that operates on a specific key.
Coder<AccumT>	getAccumulatorCoder(CoderRegistry registry, Coder<K> keyCoder, 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<K> keyCoder, Coder<InputT> inputCoder) Returns the Coder to use by default for output OutputT values, or null if it is not able to be inferred.

Methods inherited from interface org.apache.beam.sdk.transforms.display.HasDisplayData

populateDisplayData

Method Detail

getAccumulatorCoder

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

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 K keys and input 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.

Throws:

CannotProvideCoderException

getDefaultOutputCoder

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

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 K keys and input InputT values and the enclosing Pipeline's CoderRegistry to try to infer the Coder for OutputT values.

Throws:

CannotProvideCoderException

forKey

CombineFnBase.GlobalCombineFn<InputT,AccumT,OutputT> forKey(K key,
                                                            Coder<K> keyCoder)

Returns the a regular CombineFnBase.GlobalCombineFn that operates on a specific key.