Keys in PHP array are not sorted numerically

Question

I have a PHP array with keys that contain a year and week number like so:

year-week

Using the built in ksort function it's returning them like so:

ksort($array);

2011-21
2011-3
2011-44
2011-45

Is it possible to have them sorted numerically like so:

2011-3
2011-21
2011-44
2011-45

Answer 1

If you are using PHP >= 5.4 use ksort($array, SORT_NATURAL);

Answer 2

Use uksort to sort the keys, and in the callback use, strnatcmp.

uksort($array, function($a,$b){
    return strnatcmp($a,$b);
});