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.

Returns TRUE on success or FALSE on failure.

Example 1. usort() example <?php function cmp($a, $b) {     if ($a == $b) {         return 0;     }     return ($a < $b) ? -1 : 1; } $a = array(3, 2, 5, 6, 1); usort($a, "cmp"); foreach ($a as $key => $value) {     echo "$key: $value\n"; } ?> The above example will output: 0: 1 1: 2 2: 3 3: 5 4: 6

Example 2. usort() example using multi-dimensional array <?php 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. The above example will output: $fruits[0]: apples $fruits[1]: grapes $fruits[2]: lemons

Example 3. usort() example using a member function of an object <?php class TestObj {     var $name;     function TestObj($name)     {         $this->name = $name;     }     /* This is the static comparing function: */     function cmp_obj($a, $b)     {         $al = strtolower($a->name);         $bl = strtolower($b->name);         if ($al == $bl) {             return 0;         }         return ($al > $bl) ? +1 : -1;     } } $a[] = new TestObj("c"); $a[] = new TestObj("b"); $a[] = new TestObj("d"); usort($a, array("TestObj", "cmp_obj")); foreach ($a as $item) {     echo $item->name . "\n"; } ?> The above example will output: b c d

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