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Java 8 Streams - Collectors.averagingDouble Examples

Java 8 Streams Java Java API 

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Class:

java.util.stream.Collectors

java.lang.Objectjava.lang.Objectjava.util.stream.Collectorsjava.util.stream.CollectorsLogicBig

Method:

public static <T> Collector<T,?,Double> averagingDouble(ToDoubleFunction<? super T> mapper)

Returns a Collector that produces the arithmetic mean of a double-valued function applied to the input elements. If no elements are present, the result is 0.


Examples


The method Collectors#averagingDouble converts the stream elements to primitive double per user provided mapper function and returns the arithmetic mean of those doubles. 

package com.logicbig.example.collectors;


import java.math.BigDecimal;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class AveragingDoubleExample {
    public static void main (String[] args) {
        Stream<BigDecimal> s = Stream.iterate(
                            BigDecimal.ONE, bigDecimal ->
                                                bigDecimal.add(BigDecimal.ONE))
                                     .limit(10).peek(System.out::println);

        Double d = s.collect(Collectors.averagingDouble(BigDecimal::doubleValue));
        System.out.println("average: " + d);
    }
}

Output

1
2
3
4
5
6
7
8
9
10
average: 5.5
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