PHP中的数组组合器 [英] Array combinatorics in PHP

问题描述

考虑以下数组:

$a = [['x'], ['y', 'z', 'w'], ['m', 'n']];

如何从中生成以下数组:

How can generate following array from it:

$output=[
[[x][y][m]],
[[x][z][n]],
[[x][w][m]],
[[x][y][n]],
[[x][z][m]],
[[x][w][n]],
];

我正在寻找比我的代码更有效的代码. (我的当前代码显示在下面的答案中)

I am searching for a more efficient code than mine. (My current code is presented as an answer below)

推荐答案

在这里.假设:

$array = [['x'], ['y', 'z', 'w'], ['m', 'n']];

编辑:经过一些性能测试，我得出的结论是我之前发布的解决方案比OP代码慢300％，这肯定是由于嵌套的函数调用堆栈.因此，这是OP方法的改进版本，大约快了 40％:

After some performance testing, I concluded the solution I posted before is about 300% slower than OP's code, surely due to nested function call stacking. So here is an improved version of OP's approach, which is around 40% faster:

$count     = array_map('count', $array);
$finalSize = array_product($count);
$arraySize = count($array);
$output    = array_fill(0, $finalSize, []);
$i = 0;
$c = 0;
for (; $i < $finalSize; $i++) {
    for ($c = 0; $c < $arraySize; $c++) {
        $output[$i][] = $array[$c][$i % $count[$c]];
    }
}

基本上是相同的代码，但是我尽可能使用本机函数，并且还从循环中取出了一些不必在每次迭代中执行的功能.

It is basically the same code but I used native functions when possible and also took out the loops some functionality that hadn't to be executed on each iteration.

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