   #PHP Manual Array Functions uksort Aspell functions [deprecated]

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                                     usort

   (PHP 3>= 3.0.3, PHP 4 )
   usort --  Sort an array by values using a user-defined comparison
   function

Description

   void usort ( array array, callback cmp_function)

   This function will sort an array by its values using a user-supplied
   comparison function. If the array you wish to sort needs to be sorted
   by some non-trivial criteria, you should use this function.

   The comparison function must return an integer less than, equal to, or
   greater than zero if the first argument is considered to be
   respectively less than, equal to, or greater than the second.

     Note: If two members compare as equal, their order in the sorted
     array is undefined. Up to PHP 4.0.6 the user defined functions
     would keep the original order for those elements, but with the new
     sort algorithm introduced with 4.1.0 this is no longer the case as
     there is no solution to do so in an efficient way.

   Example 1. usort() example
   <?php
   function cmp($a, $b) {
       if ($a == $b) {
           return 0;
       }
       return ($a < $b) ? -1 : 1;
   }
   $a = array(3, 2, 5, 6, 1);
   usort($a, "cmp");
   while (list($key, $value) = each($a)) {
       echo "$key: $value\n";
   }
   ?>

   This example would display:
0: 1
1: 2
2: 3
3: 5
4: 6

     Note: Obviously in this trivial case the sort() function would be
     more appropriate.

   Example 2. usort() example using multi-dimensional array
   <?php
   function cmp($a, $b) {
       return strcmp($a["fruit"], $b["fruit"]);
   }
   $fruits[0]["fruit"] = "lemons";
   $fruits[1]["fruit"] = "apples";
   $fruits[2]["fruit"] = "grapes";
   usort($fruits, "cmp");
   while (list($key, $value) = each($fruits)) {
       echo "\$fruits[$key]: " . $value["fruit"] . "\n";
   }
   ?>

   When sorting a multi-dimensional array, $a and $b contain references
   to the first index of the array.

   This example would display:
$fruits[0]: apples
$fruits[1]: grapes
$fruits[2]: lemons

   Example 3. usort() example using a member function of an object
   <?php
   class TestObj {
       var $name;
       function TestObj($name) {
           $this->name = $name;
       }
       /* This is the static comparing function: */
       function cmp_obj($a, $b) {
           $al = strtolower($a->name);
           $bl = strtolower($b->name);
           if ($al == $bl) {
               return 0;
           }
           return ($al > $bl) ? +1 : -1;
       }
   }
   $a[] = new TestObj("c");
   $a[] = new TestObj("b");
   $a[] = new TestObj("d");
   usort($a, array("TestObj", "cmp_obj"));
   foreach ($a as $item) {
       echo $item->name . "\n";
   }
   ?>

   This example would display:
b
c
d

   See also uasort(), uksort(), sort(), asort(), arsort(),ksort(),
   natsort(), and rsort().
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