rsort()

(PHP 4, PHP 5, PHP 7)

对数组逆向排序

说明

rsort(array &$array[,int $sort_flags= SORT_REGULAR]): bool

本函数对数组进行逆向排序（最高到最低）。

Note:

If two members compare as equal, their relative order in the sorted array is undefined.

参数

$array

输入的数组。

$sort_flags

可以用可选参数$sort_flags改变排序的行为，详情见sort()。

返回值

成功时返回TRUE，或者在失败时返回FALSE。

范例

Example #1rsort()例

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

以上例程会输出：

0 = orange
1 = lemon
2 = banana
3 = apple

fruits 被按照字母顺序逆向排序。

注释

Note:此函数为$array中的元素赋与新的键名。这将删除原有的键名，而不是仅仅将键名重新排序。

参见

• arsort() 对数组进行逆向排序并保持索引关系
• krsort() 对数组按照键名逆向排序
• 数组排序函数对比

Like sort(), rsort() assigns new keys for the elements in array. It will remove any existing keys you may have assigned, rather than just reordering the keys. This means that it will destroy associative keys.
$animals = array("dog"=>"large", "cat"=>"medium", "mouse"=>"small");
print_r($animals);
//Array ( [dog] => large [cat] => medium [mouse] => small )
rsort($animals);
print_r($animals);
//Array ( [0] => small [1] => medium [2] => large ) 
Use KSORT() or KRSORT() to preserve associative keys.

A cleaner (I think) way to sort a list of files into reversed order based on their modification date.
<?php
  $path = $_SERVER[DOCUMENT_ROOT]."/files/";
  $dh = @opendir($path);
  while (false !== ($file=readdir($dh)))
  {
   if (substr($file,0,1)!=".")
     $files[]=array(filemtime($path.$file),$file);  #2-D array
  }
  closedir($dh);
  if ($files)
  {
   rsort($files); #sorts by filemtime
   #done! Show the files sorted by modification date
   foreach ($files as $file)
     echo "$file[0] $file[1]<br>\n"; #file[0]=Unix timestamp; file[1]=filename
  }
?>

I needed a function that would sort a list of files into reversed order based on their modification date.
Here's what I came up with:
function display_content($dir,$ext){
  $f = array();
  if (is_dir($dir)) {
    if ($dh = opendir($dir)) {
      while (($folder = readdir($dh)) !== false) {
        if (preg_match("/\s*$ext$/", $folder)) {
          $fullpath = "$dir/$folder";
          $mtime = filemtime ($fullpath);
        
          $ff = array($mtime => $fullpath);
          $f = array_merge($f, $ff);
            
      }       
        }
      
      rsort($f, SORT_NUMERIC);
      while (list($key, $val) = each($f)) {
        $fcontents = file($val, "r");
        while (list($key, $val) = each($fcontents)) 
          echo "$val\n";
      }
    }
  }
    
    closedir($dh);
}
Call it like so:
display_content("folder","extension");

Apparently rsort does not put arrays with one value back to zero. If you have an array like: $tmp = array(9 => 'asdf') and then rsort it, $tmp[0] is empty and $tmp[9] stays as is.

I thought rsort was working successfully or on a multi-dimensional array of strings that had first been sorted with usort(). But, I noticed today that the array was only partially in descending order. I tried array_reverse on it and that seems to have solved things.

If you are sorting an array from a database result set, such as MySQL for example, another approach could be to have your database sort the result set by using ORDER BY DESC, which would be the equivalent of using rsort() on the resulting array in PHP.
[Edited by moderator for clarity: googleguy at php dot net]