PHP Array Exercises : Sort an array according to another array as a priority list

Last update on May 30 2025 13:14:53 (UTC/GMT +8 hours)

20. Sort Array by Priority List

Write a PHP function to sort an array according to another array acting as a priority list.

Sample Solution:

PHP Code:

<?php
// Define a function named 'list_cmp' that compares two values based on their order in the global array '$order'
function list_cmp($a, $b)
{
    global $order;

    // Iterate through the '$order' array
    foreach ($order as $key => $value)
    {
        // If $a matches a value in '$order', return 0 to indicate equality
        if ($a == $value)
        {
            return 0;
            break;
        }

        // If $b matches a value in '$order', return 1 to indicate inequality
        if ($b == $value)
        {
            return 1;
            break;
        }
    }
}

// Define an array '$order' specifying the desired order of values
$order[0] = 1;
$order[1] = 3;
$order[2] = 4;
$order[3] = 2;

// Define an array '$array' with unsorted values
$array[0] = 2;
$array[1] = 1;
$array[2] = 3;
$array[3] = 4;
$array[4] = 2;
$array[5] = 1;
$array[6] = 2;

// Use 'usort' function to sort '$array' based on the order specified in the 'list_cmp' function
usort($array, "list_cmp");

// Print the sorted array
print_r($array);
?>

Output:

Array                                                       
(                                                           
    [0] => 1                                                
    [1] => 1                                                
    [2] => 3                                                
    [3] => 4                                                
    [4] => 2                                                
    [5] => 2                                                
    [6] => 2                                                
)     

Flowchart:

For more Practice: Solve these Related Problems:

• Write a PHP function that sorts an array based on the order of elements in a priority array provided as a parameter.
• Write a PHP script to rearrange an array by first mapping its values to a priority list then sorting accordingly.
• Write a PHP program to implement a custom comparison function that sorts an array according to priorities given in another array.
• Write a PHP script to merge two arrays—one for priorities and one for data—and then output the sorted result based on the priority positions.

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