io.github.devlibx.miscellaneous.util.aggregation

Interface AggregateFunction<IN,ACC,OUT>

All Superinterfaces:

java.io.Serializable

public interface AggregateFunction<IN,ACC,OUT>
extends java.io.Serializable

Method Summary

Modifier and Type	Method and Description
ACC	add(IN value, ACC accumulator) Adds the given input value to the given accumulator, returning the new accumulator value.
ACC	createAccumulator() Creates a new accumulator, starting a new aggregate.
OUT	getResult(ACC accumulator) Gets the result of the aggregation from the accumulator.
ACC	merge(ACC a, ACC b) Merges two accumulators, returning an accumulator with the merged state.

Method Detail

createAccumulator

ACC createAccumulator()

Creates a new accumulator, starting a new aggregate.

The new accumulator is typically meaningless unless a value is added via add(Object, Object).

The accumulator is the state of a running aggregation. When a program has multiple aggregates in progress (such as per key and window), the state (per key and window) is the size of the accumulator.

Returns:

A new accumulator, corresponding to an empty aggregate.

add

ACC add(IN value,
        ACC accumulator)

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

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

Parameters:

value - The value to add

accumulator - The accumulator to add the value to

Returns:

The accumulator with the updated state

getResult

OUT getResult(ACC accumulator)

Gets the result of the aggregation from the accumulator.

Parameters:

accumulator - The accumulator of the aggregation

Returns:

The final aggregation result.

merge

ACC merge(ACC a,
          ACC b)

Merges two accumulators, returning an accumulator with the merged state.

This function may reuse any of the given accumulators as the target for the merge and return that. The assumption is that the given accumulators will not be used any more after having been passed to this function.

Parameters:

a - An accumulator to merge

b - Another accumulator to merge

Returns:

The accumulator with the merged state