How to stable-sort a flat array by each string's trailing integer

Question

$array = array(
   'list1 - 1',
   'list7 - 1',
   'list5 - 2',
   'list3 - 1'
);

I need sort to this array numerically. The function should check the value after the equal sign for sorting.

result:

list1 - 1
list7 - 1
list3 - 1
list5 - 2

In the above result, the order is not changed either alphabetically or numerically until `list[5]`. How do I do this?

Answer 1

It looks like you want to search firstly on the trailing numbers, but if they are the same then you want to retain the original order of the items. This means a little more thinking is necessary but the job is, in essence, still very simple.

$array = array(
   'list1 - 1',
   'list7 - 1',
   'list5 - 2',
   'list3 - 1',
);

function sort_list(&$subject) {
    // Get an array of the trailing numbers to use within the callback
    $nums = preg_replace('/^.* - (\d+)$/', '$1', $subject);
    // Sort values by trailing number or key
    uksort($subject, function($a,$b) use ($nums) {
        // If numbers are the same, sort by key
        if ($nums[$a] === $nums[$b]) {
            return $a - $b;
        }
        // Othwerise sort by numbers
        return $nums[$a] - $nums[$b];
    });
}

sort_list($array);
var_dump($array);

Outputs something like:

array(4) {
  [0]=>
  string(9) "list1 - 1"
  [1]=>
  string(9) "list7 - 1"
  [3]=>
  string(9) "list3 - 1"
  [2]=>
  string(9) "list5 - 2"
}