PHP uasort Function

last modified March 13, 2025

The PHP uasort function sorts an array with a user-defined comparison function while maintaining index association. It's useful for associative arrays where key-value pairs must be preserved.

Basic Definition

The uasort function sorts an array using a callback comparison function. Unlike usort, it preserves the original array keys.

Syntax: uasort(array &$array, callable $callback): bool. The callback must return an integer less than, equal to, or greater than zero.

Basic uasort Example

This example demonstrates sorting an associative array by values while keeping the key-value associations intact.

basic_uasort.php

<?php

$fruits = [
    "a" => "lemon",
    "b" => "orange",
    "c" => "banana",
    "d" => "apple"
];

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

uasort($fruits, 'compare');

print_r($fruits);

This sorts the fruits array alphabetically by value while maintaining the original keys. The output shows the sorted array with preserved key-value pairs.

Sorting by String Length

Sort an associative array by the length of its string values while keeping the original keys.

string_length_sort.php

<?php

$words = [
    "first" => "cat",
    "second" => "elephant",
    "third" => "dog",
    "fourth" => "giraffe"
];

uasort($words, function($a, $b) {
    return strlen($a) - strlen($b);
});

print_r($words);

The array is sorted by word length in ascending order. The anonymous callback function compares string lengths to determine the order.

Sorting Objects by Property

Sort an array of objects by a specific property while maintaining the original array keys.

object_property_sort.php

<?php

class Product {
    public function __construct(
        public string $name,
        public float $price
    ) {}
}

$products = [
    "p1" => new Product("Laptop", 999.99),
    "p2" => new Product("Phone", 699.99),
    "p3" => new Product("Tablet", 399.99)
];

uasort($products, function($a, $b) {
    return $a->price <=> $b->price;
});

print_r($products);

This sorts products by price in ascending order. The spaceship operator (<=>) simplifies the comparison of numeric values.

Case-Insensitive Sorting

Perform a case-insensitive sort on an associative array while preserving the original keys.

case_insensitive_sort.php

<?php

$names = [
    "user1" => "John",
    "user2" => "alice",
    "user3" => "Bob",
    "user4" => "CHARLIE"
];

uasort($names, function($a, $b) {
    return strcasecmp($a, $b);
});

print_r($names);

The array is sorted alphabetically without considering letter case. The strcasecmp function handles the case-insensitive comparison.

Multi-Dimensional Array Sorting

Sort a multi-dimensional associative array by a specific sub-array value while maintaining the outer array keys.

multi_dimensional_sort.php

<?php

$employees = [
    "e1" => ["name" => "Alice", "salary" => 55000],
    "e2" => ["name" => "Bob", "salary" => 45000],
    "e3" => ["name" => "Charlie", "salary" => 60000]
];

uasort($employees, function($a, $b) {
    return $b["salary"] <=> $a["salary"];
});

print_r($employees);

This sorts employees by salary in descending order. The callback accesses the salary values in each sub-array for comparison.

Best Practices

Clear Callbacks: Use descriptive names for comparison functions.
Type Safety: Add type hints for robust comparison logic.
Performance: Keep comparison functions efficient for large arrays.
Consistency: Ensure comparison function returns consistent values.

Source

PHP uasort Documentation

This tutorial covered the PHP uasort function with practical examples showing its usage for sorting associative arrays while preserving keys.

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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