php - PHP：只有唯一对的嵌套循环

Question

我需要创建一个只有唯一对的数组，所以没有重复。问题是，当只是相互迭代时，由于某种原因，最后一对通常是重复的。

所以这里有一个简单的例子：

<?php 

$teams = [
    ['id' => 1],
    ['id' => 2],
    ['id' => 3],
    ['id' => 4],
];

foreach ($teams as $team_a) {
    foreach ($teams as $team_b) {
        if ($team_a['id'] !== $team_b['id']) {
            $pairs[] = [$team_a['id'], $team_b['id']];
        }
    }
}

?>

返回如下内容：

0: [1, 2]
1: [1, 3]
2: [1, 4]
3: [2, 1]
4: [2, 3]
5: [2, 4]
6: [3, 1]
7: [3, 2]
8: [3, 4]
...

所以你可以看到有些对是相同的，比如[1, 2]和[2, 1]。在半次迭代之后，只有重复。

像这样迭代并确保只有唯一对的最有效方法是什么？

谢谢！

标签： phploops

Answer 1

显然，当 key(team_a) > key(team_b) 时总是出现重复项

<?php 

$teams = [
    ['id' => 1],
    ['id' => 2],
    ['id' => 3],
    ['id' => 4],
];

foreach ($teams as $offset => $team_a) {
    foreach (array_slice($teams, $offset+1) as $team_b) {
        $pairs[] = [$team_a['id'], $team_b['id']];
    }
}