怎么样使用php实现多维数组排序？

//定义一个学生数组
$students = array(
 256=>array('name'=>'jon','grade'=>98.5),
 2=>array('name'=>'vance','grade'=>85.1),
 9=>array('name'=>'stephen','grade'=>94.0),
 364=>array('name'=>'steve','grade'=>85.1),
 68=>array('name'=>'rob','grade'=>74.6),
);
//按照名称进行排序
function name_sort($x, $y)
{
 return strcasecmp($x['name'],$y['name']);
}
//按照成绩进行排序
function grade_sort($x,$y)
{
 return ($x['grade'] > $y['grade']);
}
//应用
uasort($students, name_sort);
uasort($students, grade_sort);