PHP sort array on certain character --> 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'...

Use usort() and apply your custom sorting function to it.

Rizier123
– Rizier123

2016-08-30 19:00:11 +00:00
Commented Aug 30, 2016 at 19:00 — Rizier123
– Rizier123, Commented Aug 30, 2016 at 19:00
It works! Thank you for pointing that out!

Alexander
– Alexander

2016-08-30 19:08:14 +00:00
Commented Aug 30, 2016 at 19:08 — Alexander
– Alexander, Commented Aug 30, 2016 at 19:08

Mureinik · Accepted Answer · 2016-08-30 19:09:47Z

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 (e.g., 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, i.e., 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);
});

answered Aug 30, 2016 at 19:09

Mureinik

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1 Comment

Alexander Over a year ago

Thank you very much for your good explanation! I will be using your function. :)

AbraCadaver · Accepted Answer · 2016-08-30 19:17:14Z

1

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");

edited Aug 30, 2016 at 19:17

AbraCadaver

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answered Aug 30, 2016 at 19:12

Alexander

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Comments

Don't Panic · Accepted Answer · 2016-08-30 20:19:27Z

1

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));
});

answered Aug 30, 2016 at 20:19

Don't Panic

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