PHP uksort() Function

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:

1. $array: This parameter specifies an array which we need to sort.
2. 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