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arsort

(PHP 4, PHP 5, PHP 7, PHP 8)

arsort — 对数组进行降向排序并保持索引关系

说明

arsort(array &$array, int $flags = SORT_REGULAR): true

对 array 本身按照降序排序，并保持数组的键与值之间的关联。

主要用于对那些单元顺序很重要的结合数组进行排序。

注意:
如果两个成员完全相同，那么它们将保持原来的顺序。在 PHP 8.0.0 之前，它们在排序数组中的相对顺序是未定义的。

注意:
重置数组中的内部指针，指向第一个元素。

参数

array

输入的数组。

flags

可选的第二个参数 flags 可以用以下值改变排序的行为：

排序类型标记：

SORT_REGULAR - 正常比较单元详细描述参见比较运算符章节
SORT_NUMERIC - 单元被作为数字来比较
SORT_STRING - 单元被作为字符串来比较
SORT_LOCALE_STRING - 根据当前的区域（locale）设置来把单元当作字符串比较，可以用 setlocale() 来改变。
SORT_NATURAL - 和 natsort() 类似对每个单元以“自然的顺序”对字符串进行排序。
SORT_FLAG_CASE - 能够与 SORT_STRING 或 SORT_NATURAL 合并（OR 位运算），不区分大小写排序字符串。

返回值

总是返回 true。

更新日志

版本	说明
8.2.0	现在返回类型为 `true`；之前是 bool。

示例

示例 #1 arsort() 示例

<?php
$fruits = array("d" => "lemon", "a" => "orange", "b" => "banana", "c" => "apple");
arsort($fruits);
foreach ($fruits as $key => $val) {
    echo "$key = $val\n";
}
?>

以上示例会输出：

 
a = orange
d = lemon
b = banana
c = apple

fruits 被按照字母顺序逆向排序，并且单元的索引关系不变。

参见

sort() - 对数组升序排序
asort() - 对数组进行升序排序并保持索引关系
数组排序函数对比

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User Contributed Notes 6 notes

down

morgan at anomalyinc dot com ¶

23 years ago

If you need to sort a multi-demension array, for example, an array such as 



$TeamInfo[$TeamID]["WinRecord"] 

$TeamInfo[$TeamID]["LossRecord"] 

$TeamInfo[$TeamID]["TieRecord"] 

$TeamInfo[$TeamID]["GoalDiff"]

$TeamInfo[$TeamID]["TeamPoints"] 



and you have say, 100 teams here, and want to sort by "TeamPoints":



first, create your multi-dimensional array. Now, create another, single dimension array populated with the scores from the first array, and with indexes of corresponding team_id... ie

$foo[25] = 14

$foo[47] = 42

or whatever.

Now, asort or arsort the second array.

Since the array is now sorted by score or wins/losses or whatever you put in it, the indices are all hoopajooped.

If you just walk through the array, grabbing the index of each entry, (look at the asort example. that for loop does just that) then the index you get will point right back to one of the values of the multi-dimensional array.

Not sure if that's clear, but mail me if it isn't...

-mo

down

stephenakins at gmail dot com ¶

6 years ago

I have two servers; one running 5.6 and another that is running 7.  Using this function on the two servers gets me different results when all of the values are the same.  

<?php

$list = json_decode('{"706":2,"703":2,"702":2,"696":2,"658":2}', true);

print_r($list);

arsort($list);
echo "<br>";

print_r($list);

?>

PHP 5.6 results:
Array ( [706] => 2 [703] => 2 [702] => 2 [696] => 2 [658] => 2 ) 
Array ( [658] => 2 [696] => 2 [702] => 2 [703] => 2 [706] => 2 )

PHP 7 results:
Array ( [706] => 2 [703] => 2 [702] => 2 [696] => 2 [658] => 2 ) 
Array ( [706] => 2 [703] => 2 [702] => 2 [696] => 2 [658] => 2 )

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-1

FatBat ¶

12 years ago

Needed to get the index of the max/highest value in an assoc array.

max() only returned the value, no index, so I did this instead.



<?php

reset($x);   // optional.

arsort($x);

$key_of_max = key($x);   // returns the index.

?>

down

-6

rodders_plonker at yahoo dot com ¶

23 years ago

I was having trouble with the arsort() function on an older version of PHP which was returning an error along the lines of 'wrong perameter count for function arsort' when I tried to use a flag for numeric sorting (2/SORT_NUMERIC).

I figured, as I only wanted to sort integers, I could pad numbers from the left to a specific length with 0's (using the lpad function provided by improv@magma.ca in the notes at http://www.php.net/manual/ref.strings.php).

A string sort then correctly sorts numerically (i.e. {30,2,10,21} becomes {030,021,010,002} not {30,21,2,10}) when echoing the number an (int)$string_name hides the leading 0's.



Made my day :).



Rodders.

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-11

jordancdarwin at googlemail dot com ¶

15 years ago

A lot of people seem to trip up on this and ask me questions as to debugging. Bear in mind that this returns boolean, and does not return an array of affected items. 

$array = array("One"=>1, "Three" => 3,"Two" =>2);
print_r(asort($array));

If successful, will return 1, and error if there is a string used. Useful to note so then people stop asking me :D

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-19

sebas2day ¶

11 years ago

If you are dealing with a multidimensional array you want to sort, then this might be helpfull: 

<?php
function array_sort($arr){
    if(empty($arr)) return $arr;
    foreach($arr as $k => $a){
        if(!is_array($a)){
            arsort($arr); // could be any kind of sort
            return $arr;
        }else{
            $arr[$k] = array_sort($a);
        }
    }
    return $arr;
}
?>

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