PHP多維陣列排序

$a = Array (  
[0] => Array ( [level] => 25 [nick_name] => 王貴)  
[1] => Array ( [level] => 6 [nick_name] => 張三)  
[2] => Array ( [level] => 30 [nick_name] => 李四)  
[3] => Array ( [level] => 25 [nick_name] => 王五)  
[4] => Array ( [level] => 21 [nick_name] => 六兒)  
[5] => Array ( [level] => 9 [nick_name] => 哈哈)  
[6] => Array ( [level] => 30 [nick_name] => 呼呼)  
)

我這裡有一個數組，我想根據level的值，從大到小排列，數組結構保持不變 

===================

 方法：

$t = array();foreach($a as $v) {$t[] = $v['level'];}array_multisort($t, SORT_DESC, $a);

print_r($a);