org.apache.flink.api.common.functions

接口 ReduceFunction<T>

类型参数:

T - Type of the elements that this function processes.

所有超级接口:

Function, Serializable

所有已知实现类:

RichReduceFunction

函数接口:

这是一个函数接口, 因此可用作 lambda 表达式或方法引用的赋值目标。

@Public
 @FunctionalInterface
public interface ReduceFunction<T>
extends Function, Serializable

Base interface for Reduce functions. Reduce functions combine groups of elements to a single value, by taking always two elements and combining them into one. Reduce functions may be used on entire data sets, or on grouped data sets. In the latter case, each group is reduced individually.

For a reduce functions that work on an entire group at the same time (such as the MapReduce/Hadoop-style reduce), see GroupReduceFunction. In the general case, ReduceFunctions are considered faster, because they allow the system to use more efficient execution strategies.

The basic syntax for using a grouped ReduceFunction is as follows:

 DataSet<X> input = ...;

 DataSet<X> result = input.groupBy(<key-definition>).reduce(new MyReduceFunction());
 

Like all functions, the ReduceFunction needs to be serializable, as defined in Serializable.

方法概要

限定符和类型	方法和说明
T	reduce(T value1, T value2) The core method of ReduceFunction, combining two values into one value of the same type.

方法详细资料

reduce

T reduce(T value1,
         T value2)
  throws Exception

The core method of ReduceFunction, combining two values into one value of the same type. The reduce function is consecutively applied to all values of a group until only a single value remains.

参数:

value1 - The first value to combine.

value2 - The second value to combine.

返回:

The combined value of both input values.

抛出:

Exception - This method may throw exceptions. Throwing an exception will cause the operation to fail and may trigger recovery.