某些字符上的PHP排序数组 - > sort（$ array [2]）

Question

I would like to sort the following array on the second character [1] (1 to D):

$_SESSION['kartenstapel']=array(
                '11','12','13','14','15','16','17','18','19','1A','1B','1C','1D',
                '21','22','23','24','25','26','27','28','29','2A','2B','2C','2D',
                '31','32','33','34','35','36','37','38','39','3A','3B','3C','3D',
                '41','42','43','44','45','46','47','48','49','4A','4B','4C','4D',
                '51','52','53','54','55','56','57','58','59','5A','5B','5C','5D',
                'W1','W2','W3','W4','W5','W6','W7','W8','W9','WA','WB','WC','WD' 
  );

Ideal output would be the following:

$_SESSION['kartenstapel']=array(
                '11','21','31','41','51','W1','12','22','32','42','52','W2','13'...

Answer 1

You can use the usort function to pass your own custom comparing-function.

There are a couple of things to keep in mind here. The first thing you need to compare is the [1] character. However, naturally, D doesn't come after 1 (for example), so you'd need to do some manipulation. A neat trick is to treat this character as a hexdecimal number (eg, by using base_convert and converting it to an integer. Second, if both string's second character is the same, you'd want to sort lexicographically, ie, just return the result from strcmp . When you put it all together, you'll get something like this:

usort($_SESSION['kartenstapel'], function ($a, $b) {
    $cmp = base_convert($a[1], 16, 10) - base_convert($b[1], 16, 10);
    if ($cmp != 0) {
        return $cmp;
    }
    return strcmp($a, $b);
});

Answer 2

The following function worked for me. It was taken from and I only had to add "[1]": http://www.w3schools.com/php/showphp.asp?filename=demo_func_usort

Thanks to Rizier123.

function my_sort($a,$b){
    if ($a[1]==$b[1]) return 0;
    return ($a[1]<$b[1])?-1:1;
}

usort($_SESSION['kartenstapel'],"my_sort");

Answer 3

Since they're all only two characters, it looks like you could just sort by comparing the reverse of each string.

usort($_SESSION['kartenstapel'], function($a, $b) {
    return strcmp(strrev($a), strrev($b));
});