PHP 二维数组根据某个字段排序

$arr = array();
$arr[] = array('name' => 'a', 'flag' => 3);
$arr[] = array('name' => 'b', 'flag' => 2);
$arr[] = array('name' => 'c', 'flag' => 1);
$flag = array();
foreach ($arr as $key => $value) {
    $flag[] = $value['flag'];
}

array_multisort($flag,SORT_ASC,$arr);
echo "
";
var_dump($arr);