PHP实现排列组合，获取数据组合出现的可能情况

有个需求是差不多数学组合。
如1 2 3，2个数字为一个组合，可以组合多少种不同的情况。
结果要求为

• 1 2
• 1 3
• 2 3
  这三种情况

function combination($array, $length) {
    $result = [];
    //取出数据要求总长度不符合 则直接返回空数组
    $number = count($array);
    if ($length <= 0 || $length > $number) {
        return $result;
    }
    //循环开始
    foreach ($array as $key => $value) {
        $temp = [ $value ];
        if ($length == 1) { //如果长度为了 则直接返回所有数据单个值组成的数组
            $result[] = $temp;
        } else {
            //从当前值开始向后截取数组
            $less = array_slice($array, $key + 1);
            $small = combination($less, $length - 1);
            foreach ($small as $smallValue) {
                $result[] = array_merge($temp, $smallValue);
            }
        }
    }
    return $result;
}

$array = range(1,5);
combination($array,3);

打印结果

Array
(
    [0] => Array
        (
            [0] => 1
            [1] => 2
            [2] => 3
        )

    [1] => Array
        (
            [0] => 1
            [1] => 2
            [2] => 4
        )

    [2] => Array
        (
            [0] => 1
            [1] => 2
            [2] => 5
        )

    [3] => Array
        (
            [0] => 1
            [1] => 3
            [2] => 4
        )

    [4] => Array
        (
            [0] => 1
            [1] => 3
            [2] => 5
        )

    [5] => Array
        (
            [0] => 1
            [1] => 4
            [2] => 5
        )

    [6] => Array
        (
            [0] => 2
            [1] => 3
            [2] => 4
        )

    [7] => Array
        (
            [0] => 2
            [1] => 3
            [2] => 5
        )

    [8] => Array
        (
            [0] => 2
            [1] => 4
            [2] => 5
        )

    [9] => Array
        (
            [0] => 3
            [1] => 4
            [2] => 5
        )

)