是否有一些仅流的方法来确定最大流元素的索引？ [英] Is There Some Stream-Only Way To Determine The Index Of The Max Stream Element?

问题描述

我有一个 Stream< Set< Integer>> intSetStream 。

我可以这样做...

Set<Integer> theSetWithTheMax = intSetStream.max( (x,y)->{ return Integer.compare( x.size(), y.size() ); } ).get( );

...我得到了 Set< Integer> 其中包含 Integer 元素的数量最多。

...and I get a hold of the Set<Integer> that has the highest number of Integer elements in it.

这很棒。但我真正需要知道的是，这是流中的第一个 Set 这是最大值？或者它是 Stream 中的第10个 Set ？或 i th 设置？其中哪一个元素最多？

That's great. But what I really need to know is, is it the 1st Set in that Stream that's the max? Or is it the 10th Set in the Stream? Or the ith Set? Which one of them has the most elements in it?

所以我的问题是：有没有办法 - 使用Stream API - 我可以在 Stream i 设置对于 Set.size（）调用，c $ c> of Set s返回所有值的最大值？

So my question is: Is there some way — using the Stream API — that I can determine "It was the ith Set in the Stream of Sets that returned the largest value of them all, for the Set.size( ) call"?

我能想到的最佳解决方案是迭代 Stream< Set< Integer>> （使用 intSetStream.iterator（））并进行手动滚动的 max（）计算。但我希望能够学习更多 Stream -y方式来实现它;如果有这样的话。

The best solution I can think of, is to iterate over the Stream<Set<Integer>> (using intSetStream.iterator()) and do a hand-rolled max( ) calculation. But I'm hoping to learn a more Stream-y way to go about it; if there is such a thing.

推荐答案

一种方法是首先映射 Stream< Set< ;整数>> 到集合<整数> 其中每个元素的大小是每个 Set< Integer> 然后你可以提取给出 Stream< Set< Integer>> 的最大元素数量，然后得到这个集合的索引通过查找大小集合中最大数字的索引。

One way to do it is to firstly map Stream<Set<Integer>> to a Collection<Integer> where each element is the size of each Set<Integer> and then you can extract what is the largest number of elements given Stream<Set<Integer>> and then get the "index" of this set by finding an index of the largest number in the collection of sizes.

请考虑以下示例：

import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class IntSetStreamExample {

    public static void main(String[] args) {

        final Stream<Set<Integer>> stream = Stream.of(
                new HashSet<>(Arrays.asList(1,2,3)),
                new HashSet<>(Arrays.asList(1,2)),
                new HashSet<>(Arrays.asList(1,2,3,4,5)),
                new HashSet<>(Arrays.asList(0)),
                new HashSet<>(Arrays.asList(0,1,2,3,4,5)),
                new HashSet<>()
        );

        final List<Integer> result = stream.map(Set::size).collect(Collectors.toList());

        System.out.println("List of number of elements in Stream<Set<Integer>>: " + result);

        final int max = Collections.max(result);

        System.out.println("Largest set contains " + max + " elements");

        final int index = result.indexOf(max);

        System.out.println("Index of the largest set: " + index);
    }
}

示例输出可能如下所示：

The exemplary output may look like this:

List of number of elements in Stream<Set<Integer>>: [3, 2, 5, 1, 6, 0]
Largest set contains 6 elements
Index of the largest set: 4

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