usort

Description

This function will sort an array by its values using a user-supplied comparison function. If the array you wish to sort needs to be sorted by some non-trivial criteria, you should use this function.

The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second. If two members compare as equal, their order in the sorted array is undefined.

Example 1. Usort() example function cmp ($a, $b) { if ($a == $b) return 0; return ($a > $b) ? -1 : 1; } $a = array (3, 2, 5, 6, 1); usort ($a, "cmp"); while (list ($key, $value) = each ($a)) { echo "$key: $value\n"; }

This example would display:

0: 6
1: 5
2: 3
3: 2
4: 1
      

Example 2. Usort() example using multi-dimensional array function cmp ($a, $b) { return strcmp($a["fruit"],$b["fruit"]); } $fruits[0]["fruit"] = "lemons"; $fruits[1]["fruit"] = "apples"; $fruits[2]["fruit"] = "grapes"; usort($fruits, "cmp"); while (list ($key, $value) = each ($fruits)) { echo "\$fruits[$key]: " . $value["fruit"] . "\n"; }

When sorting a multi-dimensional array, $a and $b contain references to the first index of the array.

This example would display:

$fruits[0]: apples
$fruits[1]: grapes
$fruits[2]: lemons
      

See also: uasort(), uksort(), sort(), asort(), arsort(),ksort(), natsort(), and rsort().