org.apache.flink.api.common.functions

Interface CombineFunction<IN,OUT>

Type Parameters:

IN - The data type processed by the combine function.

OUT - The data type emitted by the combine function.

All Superinterfaces:

Function, Serializable

@Public
public interface CombineFunction<IN,OUT>
extends Function, Serializable

Generic interface used for combine functions ("combiners"). Combiners act as auxiliaries to a GroupReduceFunction and "pre-reduce" the data. The combine functions typically do not see the entire group of elements, but only a sub-group.

Combine functions are frequently helpful in increasing the program efficiency, because they allow the system to reduce the data volume earlier, before the entire groups have been collected.

This special variant of the combine function reduces the group of elements into a single element. A variant that can return multiple values per group is defined in GroupCombineFunction.

Method Summary

Modifier and Type	Method and Description
OUT	combine(Iterable<IN> values) The combine method, called (potentially multiple timed) with subgroups of elements.

Method Detail

combine

OUT combine(Iterable<IN> values)
     throws Exception

The combine method, called (potentially multiple timed) with subgroups of elements.

Parameters:

values - The elements to be combined.

Returns:

The single resulting value.

Throws:

Exception - The function may throw Exceptions, which will cause the program to cancel, and may trigger the recovery logic.