PHP uksort Function

last modified March 13, 2025

The PHP uksort function sorts an array by keys using a user-defined comparison function. It maintains key-value associations during sorting.

Basic Definition

The uksort function sorts an array by keys using a callback comparison function. It modifies the original array and returns true on success.

Syntax: uksort(array &$array, callable $callback): bool. The callback compares two keys and returns an integer less than, equal to, or greater than zero.

Basic uksort Example

This example demonstrates sorting an associative array by keys in ascending order.

basic_uksort.php

<?php

$data = [
    "banana" => 3,
    "apple" => 2,
    "orange" => 5
];

uksort($data, function($a, $b) {
    return strcmp($a, $b);
});

print_r($data);

Output shows the array sorted alphabetically by keys. The callback uses strcmp for string comparison. Keys maintain their values.

Reverse Key Sorting

Sort array keys in descending order by modifying the comparison logic.

reverse_uksort.php

<?php

$data = [
    "banana" => 3,
    "apple" => 2,
    "orange" => 5
];

uksort($data, function($a, $b) {
    return strcmp($b, $a); // Reverse comparison
});

print_r($data);

This reverses the key order by swapping $a and $b in strcmp. The output shows keys from "orange" to "apple".

Numeric Key Sorting

Sort numeric keys with custom comparison logic for different sorting needs.

numeric_uksort.php

<?php

$data = [
    10 => "ten",
    2 => "two",
    5 => "five"
];

uksort($data, function($a, $b) {
    return $a <=> $b; // Spaceship operator for numeric comparison
});

print_r($data);

The spaceship operator (<=>) provides clean numeric comparison. Output shows keys sorted from 2 to 10 with their corresponding values.

Case-Insensitive Sorting

Sort keys case-insensitively by modifying the string comparison approach.

case_insensitive_uksort.php

<?php

$data = [
    "Banana" => 3,
    "apple" => 2,
    "Orange" => 5
];

uksort($data, function($a, $b) {
    return strcasecmp($a, $b); // Case-insensitive comparison
});

print_r($data);

strcasecmp ignores case differences. Output shows "apple" first despite lowercase, followed by "Banana" and "Orange" in alphabetical order.

Custom Key Sorting Logic

Implement complex sorting logic based on key characteristics or patterns.

custom_uksort.php

<?php

$data = [
    "file1.txt" => "Content 1",
    "file10.txt" => "Content 10",
    "file2.txt" => "Content 2"
];

uksort($data, function($a, $b) {
    $numA = intval(preg_replace('/[^0-9]/', '', $a));
    $numB = intval(preg_replace('/[^0-9]/', '', $b));
    return $numA <=> $numB;
});

print_r($data);

This extracts numbers from filenames for natural sorting. Output shows files ordered by their numeric parts (1, 2, 10) rather than lexicographically.

Best Practices

Consistent Returns: Ensure callback always returns integer.
Performance: Avoid complex logic in large-array callbacks.
Readability: Use named functions for complex comparisons.
Type Safety: Add type hints if keys have specific types.

Source

PHP uksort Documentation

This tutorial covered the PHP uksort function with practical examples showing various key sorting scenarios and custom comparison logic.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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