怎样把一维数组的每四位作为一个单元转成二维数组？

$o = range  (1,50);
print_r ($o);
 
$new =array ();
for ($i=0; $i<count($o); $i=$i+4) {
    $new[]  = array_slice($o,  $i,  4);
}
print_r ($new);
exit;

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 4
    [4] => 5
    [5] => 6
    [6] => 7
    [7] => 8
    [8] => 9
    [9] => 10
)
Array
(
    [0] => Array
        (
            [0] => 1
            [1] => 2
            [2] => 3
            [3] => 4
        )
 
    [1] => Array
        (
            [0] => 5
            [1] => 6
            [2] => 7
            [3] => 8
        )
 
    [2] => Array
        (
            [0] => 9
            [1] => 10
        )
 
)