使用usort()和strcmp对二维数组进行排序

<?php
/**
// * Created by PhpStorm.
// * User: hp
// * Date: 2019/3/29
// * Time: 11:17
// */
echo '<pre>';
$arr = [
['name'=>'jesse','day'=>527,'age'=>10],
['name'=>'clancy','day'=>814,'age'=>17],
['name'=>'kiwi','day'=>612,'age'=>21]
];
echo '排序前'.var_export($arr,true),'<hr>';

usort($arr,function($a,$b)
{
//    return strcmp($a['day'],$b['day']);
   return strcmp($a['age'],$b['age']);
});
echo '排序之后:',var_export($arr,true),'<hr>';