How does usort() sort a two-dimensional array in descending order?

Question

How to sort a two-dimensional array in descending order with usort()

Answer 1

$stu = [
    ['name'=>'周天子', 'grade'=>'99'],
    ['name'=>'汉高祖', 'grade'=>'73'],
    ['name'=>'秦始皇', 'grade'=>'95'],
];
//输出原始数组
echo var_export($stu, true),'<hr>';

//用户自定义回调来进行排序（降序）
usort($stu, function ($m, $n){
    return strcmp($n['grade'], $m['grade']);    // strcmp()函数 （本函数返回： 0 如果两个字符串相等， <0 如果 string1 小于 string2, >0 如果string1 大于 string2
});
//输出排序后的数组
echo var_export($stu, true),'<hr>';

Answer 2

You can refer to it,

<?php

function test($array=array(),$key='',$paixu=true){

$result=array();

foreach($array as $k => $v){

$values[$k]= isset( $v[$key]) ? $v[$key] : '';

}

unset($v);

$paixu ? asort($values ) : arsort($values);

foreach ($values ​​as $k => $v){

$result[$k] = $array[ $k];

}

return $result;

}

$data = array(

array('post_id'=>1,'title'=>'How to learn PHP well','reply_num'=>582),

array('post_id'=>2,'title '=>'Summary of common functions for PHP arrays','reply_num'=>182),

array('post_id'=>3,'title'=>'Summary of common functions for PHP strings ','reply_num'=>982),

);

## $paixuhou=test($data,'reply_num',true);

echo "<pre>";

print_r($paixuhou);

?>

Answer 3

is rsort(), you used the wrong function.