Access array key using uasort in PHP

Question

If have a rather basic uasort function in PHP that looks like this:

uasort($arr, function($a, $b) {
                if ($a > $b)
                    return -1;
                if ($a < $b)
                    return 1;
...
}

The array I'm trying to sort looks like the following:

{[1642] => 1, [9314] => 4, [1634] => 3 ...}

It contains integers that are my main comparison criteria. However, if the integers are equal, then I would like to access their key values, inside the uasort function and do some magic with it to figure out the sorting from there.

I have no clue how to do that as it seems that the $a and $b variables that get passed into the function are just the integers without the corresponding keys but there should be a way to access the key as well since I'm using a function to actually preserve the keys. Any ideas?

Answer 1

uksort($arr, function ($a, $b) use ($arr) {
    return $arr[$a] - $arr[$b] ?: $a - $b;
});

You can get the values by the keys, so use uksort which gives you the keys. Replace $a - $b with your appropriate magic, here it's just sorting by the key's value.

Answer 2

The use directive (in deceze's solution) does not work in my old PHP 5.3.1 installation, while this will deliver the result:

$arr=array('1642'=>1,'9314'=>2,'1634'=>1,'1633'=>5,'1636'=>7,'1610'=>1);
print_r($arr);

function mycmp($a, $b) {
 if ($a > $b)  return -1;
 if ($a < $b)  return 1;
 else return 0;
}
function mysrt($arr){
 foreach ($arr as $k => $v) $new[$k]="$v $k";
 uasort($new, 'mycmp'); $ret=array();
 foreach ($new as $k => $v) $ret[$k]=$arr[$k];
 return $ret;
}
print_r(mysrt($arr));

mysrt() does not sort 'in-place' but will return the sorted array. And of course: my "magic" on the key sorting is rather basic. Keys will get sorted in the same way as the values. By modifying the statement $new[$k]="$v $k"; you can change the behaviour to suit your needs.

as a side note ...

deceze's solution will work on my server only when I use use(&$arr) instead of use($arr):

uksort($arr, function ($a, $b) use(&$arr) {
    return $arr[$a] - $arr[$b] ? $arr[$a] - $arr[$b] : $a - $b;
});