通过流转换数组的数组

Question

我有一个数组，例如

int[][] weights = {{1, 3, 2}, {2, 1, 4}, {2, 3, 3}, {3, 4, 2}, {4, 2, 1}};

我需要从每个数组中获取{x, y, z}两个数组{x, y, z}和{y, x, z}。像这样的东西

int[][] resultWeights = {{1, 3, 2}, {3, 1, 2}, {2, 1, 4}, {1, 2, 4} ... 

如何通过流来完成？

Answer 1

我需要从每个数组中获取{x, y, z}两个数组{x, y, z}和{y, x, z}。

迭代您的源并显式创建新条目：

int[][] weights = ...
// Every entry yields two
int[][] resultWeights = new int[weights.length * 2][];

// Iterate all entries
int i = 0;
for (int[] entry : weights) {
    // Copy entry
    resultWeights[i] = entry;
    i++;
    // Other version
    resultWeights[i] = new int[] { entry[1], entry[0], entry[2] };
    i++;
}

请注意，您可以resultWeights[i++]这样做。但对于一些程序员来说可能比较陌生。

正如您特别要求的流：

int[][] weights = ...
int[][] resultWeights = Arrays.stream(weights)
    .flatMap(entry -> Stream.of(entry, new int[] { entry[1], entry[0], entry[2] }))
    .toArray(int[][]::new);