在PHP中，如何将字符串中的字母和数字拆分为两个数组

$str = "abc123def456";
$letters = preg_split('/[^a-zA-Z]+/', $str, -1, PREG_SPLIT_NO_EMPTY);
$numbers = preg_split('/[^0-9]+/', $str, -1, PREG_SPLIT_NO_EMPTY);

print_r($letters);
print_r($numbers);

Array
(
    [0] => abc
    [1] => def
)
Array
(
    [0] => 123
    [1] => 456
)

$str = "abc123def456";
$letters = str_split(preg_replace('/[^a-zA-Z]+/', '', $str));
$numbers = str_split(preg_replace('/[^0-9]+/', '', $str));

print_r($letters);
print_r($numbers);

Array
(
    [0] => a
    [1] => b
    [2] => c
    [3] => d
    [4] => e
    [5] => f
)
Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 4
    [4] => 5
    [5] => 6
)