usort

<?

function myfunction($a, $b)
{
    if($a < $b)
    {
        return -1;
    }
    else if($a > $b)
    {
        return 1;
    }
    else
    {
        return 0;
    }
}

$array = array(3, 2, 5, 6, 1);
$callback = "myfunction";

usort($array, $callback);

print_r($array);

?>

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 5
    [4] => 6
)

<?

function myfunction($a, $b)
{
    return strcmp($a, $b);
}

$array[0] = "lemons";
$array[1] = "apples";
$array[2] = "grapes";
$callback = "myfunction";

usort($array, $callback);

foreach($array as $key => $value)
{
    echo "\$array[$key]: $value\n";
}

?>

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

<?

class myclass
{
    var $name;

    function __construct($name)
    {
        $this->name = $name;
    }

    static function myfunction($a, $b)
    {
        $al = strtolower($a->name);
        $bl = strtolower($b->name);

        if($al == $bl)
        {
            return 0;
        }

        return ($al > $bl) ? 1 : -1;
    }
}

$array[] = new myclass("c");
$array[] = new myclass("b");
$array[] = new myclass("d");
$callback = array("myclass", "myfunction");

usort($array, $callback);

foreach($array as $item)
{
    echo $item->name . "\n";
}

?>

b
c
d

<?

function myfunction($key)
{
    return function($a, $b) use ($key)
    {
        return strnatcmp($a[$key], $b[$key]);
    };
}

$array[0] = array('key_a' => 'z', 'key_b' => 'c');
$array[1] = array('key_a' => 'x', 'key_b' => 'b');
$array[2] = array('key_a' => 'y', 'key_b' => 'a');
$callback = myfunction('key_b');

usort($array, $callback);

foreach($array as $item)
{
    echo $item['key_a'] . ', ' . $item['key_b'] . "\n";
}

?>

y, a
x, b
z, c