分组值序列 [英] Group sequences of values

问题描述

我想知道是否有任何漂亮的方式使用新的Stream API来分组值序列。

I'm wondering if there's in any nifty way to use the new Stream APIs to "group" sequences of values.

例如。将一系列整数拆分为整数组，其中每个组都是一个递增的数字序列：

e.g. split a series of integers, into groups of integers where each group is an ascending number sequence:

IntStream seq = IntStream.of(1, 2, 3, -1, -1, 1, 2, 1, 2);
IntFunction next = i -> i + 1;

// DESIRED OUTPUT: [[1,2,3], [-1], [-1], [1,2], [1,2]]

推荐答案

不幸的是，Stream API不太适合解决涉及相关操作的问题在Stream元素上，就像这个一样。

Unfortunately, the Stream API is not very well suited to tackle problems that involve dependant operations on the Stream element, like this one.

但是，你可以使用 StreamEx 库：

public static void main(String[] args) {
    IntStream seq = IntStream.of(1, 2, 3, -1, -1, 1, 2, 1, 2);
    IntUnaryOperator next = i -> i + 1;

    List<List<Integer>> result = 
        IntStreamEx.of(seq).boxed().groupRuns((i1, i2) -> next.applyAsInt(i1) == i2).toList();

    System.out.println(result); // prints "[[1, 2, 3], [-1], [-1], [1, 2], [1, 2]]"
}

这个分组为 List 所有连续的整数，其中第二个整数等于 next 函数应用于第一个。最后，此流被收集到列表。

This groups into a List all consecutive integers where the second one is equal to the next function applied to the first one. Finally, this Stream is collected into a List.

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