PHP usort() Function

PHP comes with a number of built-in functions that are used to sort arrays in an easier way. Here, we are going to discuss a new function usort(). The usort() function in PHP sorts a given array by using a user-defined comparison function. This function is useful in case if we want to sort the array in a new manner. This function assigns new integral keys starting from zero to the elements present in the array and the old keys are lost. Syntax:

boolean usort( $array, "function_name");

Parameters: This function accepts two parameters as shown in the above syntax and are described below:

1. $array: This parameter specifies the array which u want to sort.
2. function_name : This parameter specifies the name of a user-defined function which compares the values and sort the array specified by the parameter $array. This function returns an integer value based on the following conditions. If two arguments are equal, then it returns 0, If first argument is greater than second, it returns 1 and if first argument is smaller than second, it returns -1.

Return Value: This function returns the boolean type of value. It returns TRUE in case of success and FALSE in case of failure. Below program illustrate the usort() function in PHP: PHP

<?php

    // PHP program to illustrate usort() function

    // This is the user-defined function used to compare
    // values to sort the input array
    function comparatorFunc( $x, $y)
    {   
        // If $x is equal to $y it returns 0
        if ($x== $y)
            return 0;
    
        // if x is less than y then it returns -1
        // else it returns 1    
        if ($x < $y)
            return -1;
        else
            return 1;
    }
    
    // Input array
    $arr= array(2, 9, 1, 3, 5); 

    usort($arr, "comparatorFunc");
    
    print_r($arr);

?>

Output:

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 5
    [4] => 9
)

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