PHP二维数组如何根据某个字段排序

<?php 
/** 
* 二维数组根据某个字段排序 
* 功能：按照用户的年龄倒序排序 
* @author ruxing.li
* @edit www.jbxue.com
*/ 
header('Content-Type:text/html;Charset=utf-8'); 
$arrUsers = array( 
array( 
'id' => 1, 
'name' => '张三', 
'age' => 25,
), 
array( 
'id' => 2, 
'name' => '李四', 
'age' => 23,
), 
array( 
'id' => 3, 
'name' => '王五', 
'age' => 40,
), 
array( 
'id' => 4, 
'name' => '赵六', 
'age' => 31,
), 
array( 
'id' => 5, 
'name' => '黄七', 
'age' => 20,
),
);
$sort = array( 
'direction' => 'SORT_DESC', //排序顺序标志 SORT_DESC 降序；SORT_ASC 升序 
'field' => 'age', //排序字段 
); 
$arrSort = array(); 
foreach($arrUsers AS $uniqid => $row){ 
foreach($row AS $key=>$value){ 
$arrSort[$key][$uniqid] = $value; 
} 
} 
if($sort['direction']){ 
array_multisort($arrSort[$sort['field']], constant($sort['direction']), $arrUsers); 
}
var_dump($arrUsers);
/*
输出结果：
array (size=5) 
0 => 
array (size=3) 
'id' => int 5 
'name' => string '黄七' (length=6) 
'age' => int 20 
1 => 
array (size=3) 
'id' => int 2 
'name' => string '李四' (length=6) 
'age' => int 23 
2 => 
array (size=3) 
'id' => int 1 
'name' => string '张三' (length=6) 
'age' => int 25 
3 => 
array (size=3) 
'id' => int 4 
'name' => string '赵六' (length=6) 
'age' => int 31 
4 => 
array (size=3) 
'id' => int 3 
'name' => string '王五' (length=6) 
'age' => int 40
*/