利用usort回调方法把二维数组通过grade按升序排列

<?php

header("Content-Type:text/html; charset=utf8");

$stu = [
   ['name' =>'林熙蕾','grade'=> 90],
   ['name' =>'范冰冰','grade'=>87],
   ['name' =>'小青',  'grade'=>73],
];

//升序回调

usort($stu,function($m,$n){

    return  strcmp($m['grade'],$n['grade']);

});

echo var_export($stu,true),'<hr>';

?>