Perhaps...
$a = explode(',', '1.1.51,1.1.51.10,1.1.51.2,1.1.51.3,1.1.51.4,A,1.1.52');
echo 'original <pre> ' . print_r($a, 1) . '</pre>';
sort($a);
echo 'after sort() <pre> ' . print_r($a, 1) . '</pre>';
natsort($a);
echo 'after natsort() <pre> ' . print_r($a, 1) . '</pre>';
giving...
original
Array
(
[0] => 1.1.51
[1] => 1.1.51.10
[2] => 1.1.51.2
[3] => 1.1.51.3
[4] => 1.1.51.4
[5] => A
[6] => 1.1.52
)
after sort()
Array
(
[0] => 1.1.51
[1] => 1.1.51.10
[2] => 1.1.51.2
[3] => 1.1.51.3
[4] => 1.1.51.4
[5] => 1.1.52
[6] => A
)
after natsort()
Array
(
[0] => 1.1.51
[2] => 1.1.51.2
[3] => 1.1.51.3
[4] => 1.1.51.4
[1] => 1.1.51.10
[5] => 1.1.52
[6] => A
)