PHP 多个一维数组组合

function A($a , $currentArr, $currentIndex , $new , &$data = []){
    foreach ($currentArr as $k=>$v){
        $new[$currentIndex] = $v;
        if (isset($a[$currentIndex +1 ])){
            A($a,$a[$currentIndex + 1 ], $currentIndex + 1 , $new , $data);
        }else{
            $data[] = $new;
        }
    }
}

$arr = [
    ['a', 'b', 'c'],
    ['d', 'e', 'f'],
    ['g', 'h', 'i'],
];
function getUnion($arr1, $arr2)
{
    $new = [];
    foreach ($arr1 as $k => $v) {
        if (!empty($arr2)) {
            foreach ($arr2 as $key => $value) {
                $new[] = $v . $value;
            }
        } else {
            $new = $arr1;
        }
    }
    return $new;
}
$result = [];
$length = count($arr);
for ($i = 0; $i < $length; $i++) {
    if ($i === 1) {
        $result = getUnion($arr[0], $arr[1]);
    }
    if ($i > 1) {
        $result = getUnion($result, $arr[$i]);
    }
}