PHP array_udiff_uassoc Function

last modified March 13, 2025

The PHP array_udiff_uassoc function computes the difference of arrays with additional index check, using callbacks for both data and index comparison. It's useful for complex array comparisons.

Basic Definition

The array_udiff_uassoc function compares arrays by values and keys. It uses two callback functions - one for value comparison and another for key comparison.

Syntax: array_udiff_uassoc(array $array1, array $array2, ..., callable $value_compare_func, callable $key_compare_func): array. Returns values from array1 not present in other arrays.

Basic array_udiff_uassoc Example

This shows a simple comparison of two arrays with custom comparison functions.

basic_array_udiff_uassoc.php

<?php

declare(strict_types=1);

function compareValues($a, $b): int {
    return $a <=> $b;
}

function compareKeys($a, $b): int {
    return strcasecmp($a, $b);
}

$array1 = ["a" => 1, "b" => 2, "c" => 3];
$array2 = ["A" => 1, "B" => 5, "C" => 3];

$result = array_udiff_uassoc($array1, $array2, 'compareValues', 'compareKeys');

print_r($result);

This compares arrays case-insensitively for keys and normally for values. Only the element with key "b" and value 2 is in array1 but not array2.

Comparing Objects with Custom Logic

Compare arrays of objects using custom comparison functions for properties.

object_comparison.php

<?php

declare(strict_types=1);

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

function compareProducts($a, $b): int {
    return $a->price <=> $b->price;
}

function compareKeys($a, $b): int {
    return strcmp($a, $b);
}

$products1 = [
    "p1" => new Product("Laptop", 999.99),
    "p2" => new Product("Phone", 699.99)
];

$products2 = [
    "p1" => new Product("Tablet", 399.99),
    "p3" => new Product("Monitor", 299.99)
];

$result = array_udiff_uassoc($products1, $products2, 'compareProducts', 'compareKeys');

print_r($result); // Outputs both products from $products1

This compares products by price and keys normally. Since no products in array1 have matching prices in array2, both are returned in the result.

Case-Insensitive String Comparison

Perform case-insensitive comparison for both keys and values.

case_insensitive.php

<?php

declare(strict_types=1);

function compareValues($a, $b): int {
    return strcasecmp($a, $b);
}

function compareKeys($a, $b): int {
    return strcasecmp($a, $b);
}

$array1 = ["Name" => "John", "Age" => "30"];
$array2 = ["name" => "JOHN", "age" => "25"];

$result = array_udiff_uassoc($array1, $array2, 'compareValues', 'compareKeys');

print_r($result);

This performs case-insensitive comparison for both keys and values. Only the Age element differs between arrays when compared this way.

Multi-Dimensional Array Comparison

Compare multi-dimensional arrays with custom comparison logic.

multi_dimensional.php

<?php

declare(strict_types=1);

function compareValues($a, $b): int {
    return $a['score'] <=> $b['score'];
}

function compareKeys($a, $b): int {
    return $a <=> $b;
}

$students1 = [
    101 => ['name' => 'Alice', 'score' => 85],
    102 => ['name' => 'Bob', 'score' => 90]
];

$students2 = [
    101 => ['name' => 'Alice', 'score' => 80],
    103 => ['name' => 'Charlie', 'score' => 95]
];

$result = array_udiff_uassoc($students1, $students2, 'compareValues', 'compareKeys');

print_r($result); // Outputs both students from $students1

This compares student records by their score values. Since no students in array1 have matching scores in array2, both are included in the result.

Complex Custom Comparison

Implement complex comparison logic combining multiple factors.

complex_comparison.php

<?php

declare(strict_types=1);

function compareValues($a, $b): int {
    $scoreA = $a['points'] * $a['multiplier'];
    $scoreB = $b['points'] * $b['multiplier'];
    return $scoreA <=> $scoreB;
}

function compareKeys($a, $b): int {
    return strlen($a) <=> strlen($b);
}

$data1 = [
    "user1" => ['points' => 10, 'multiplier' => 2],
    "longuser" => ['points' => 5, 'multiplier' => 3]
];

$data2 = [
    "usr" => ['points' => 10, 'multiplier' => 2],
    "user" => ['points' => 5, 'multiplier' => 4]
];

$result = array_udiff_uassoc($data1, $data2, 'compareValues', 'compareKeys');

print_r($result);

This compares data by calculated score (points * multiplier) and keys by length. Only the first element differs when compared this way.

Best Practices

Consistent Callbacks: Ensure comparison functions return consistent results.
Type Safety: Add type hints to callback functions for robustness.
Performance: Optimize callbacks for large array comparisons.
Readability: Use descriptive names for callback functions.

Source

PHP array_udiff_uassoc Documentation

This tutorial covered the PHP array_udiff_uassoc function with practical examples showing its usage for complex array comparisons.

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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