PHP uksort() Function

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The uksort() function is a built-in function in PHP and is used to sort an array according to the keys and not values using a user-defined comparison function.

Syntax:

boolean uksort($array, myFunction);

Parameter: This function accepts two parameters and are described below:

$array: This parameter specifies an array which we need to sort.
myFunction: This parameter specifies name of a user-defined function which will be used to sort the keys of array $array. This comparison function must return an integer.

Return value: This function returns a boolean value. It returns TRUE on success or FALSE on failure.

Below programs illustrate the uksort() function in PHP:

Program 1:

<?php 
  
// user-defined comparison function 
function my_sort($x, $y) 
{ 
    if ($x == $y)  
        return 0; 
  
    return ($x > $y) ? -1 : 1; 
} 
  
// Input array 
$names = array( 
                "10" => "javascript", 
                "20" => "php",  
                "60" => "vbscript", 
                "40" => "jsp"
              ); 
  
uksort($names, "my_sort"); 
  
// printing sorted array 
print_r ($names); 
?> 

Output:

Array
(
    [60] => vbscript
    [40] => jsp
    [20] => php
    [10] => javascript
)

Program 2:

<?php 
  
// user-defined comparison function 
function my_sort($x, $y) 
{ 
    if ($x == $y)  
        return 0; 
  
    return ($x > $y) ? 1 : -1; 
} 
  
// Input array 
$names = array( 
                "10" => "javascript", 
                "20" => "php",  
                "60" => "vbscript", 
                "40" => "jsp"
              ); 
  
uksort($names, "my_sort"); 
  
// printing sorted array 
print_r ($names); 
?> 

Output:

Array
(
    [10] => javascript
    [20] => php
    [40] => jsp
    [60] => vbscript
)

Note: If two values are compared as equal according to the user-defined comparison function then their order in the output array will be undefined.

Reference:
http://php.net/manual/en/function.uksort.php