具有优先级的PHP置换数组

这里我有一个代码，它提供了我所需的输出，但我想在选择它时添加优先级顺序

所有可能的组合码

$array = array('x2', 'y', 'm');

function depth_picker($arr, $temp_string, &$collect) {
    if ($temp_string != "") 
        $collect []= $temp_string;

    for ($i=0; $i<sizeof($arr);$i++) {
        $arrcopy = $arr;
        $elem = array_splice($arrcopy, $i, 1); // removes and returns the ith element
        if (sizeof($arrcopy) > 0) {
            depth_picker($arrcopy, $temp_string ." " . $elem[0], $collect);
        } else {
            $collect []= $temp_string. " " . $elem[0];
        }   
    }   
}

$collect = array();
depth_picker($array, "", $collect);
print_r($collect);

同样地

function array_permutation(array $array)
{
        $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++) {
             print $output[$i][] = $array[$c][$i % $count[$c]];


            }
             print "<br/>";
        }

    return $output;

}

$array = [['x2','x1'], ['y','k'], ['m', 'n']];
//print $output;
$output= array_permutation($array);

x2
x1
y
k
m
n
x2y
x1y
x2k
x1k
x2ym
x1ym
x2yn
x1yn
x2km
x1km
x2kn
x1kn