PHP array_udiff Function

last modified March 13, 2025

The PHP array_udiff function computes the difference of arrays using a callback function for data comparison. It's useful for custom comparisons.

Basic Definition

The array_udiff function compares array values using a callback. It returns values from the first array not present in other arrays.

Syntax: array_udiff(array $array1, array $array2, ..., callable $value_compare_func): array. The callback must return an integer less than, equal to, or greater than zero.

Basic array_udiff Example

This shows a simple comparison of arrays containing numbers using a callback.

basic_array_udiff.php

<?php

declare(strict_types=1);

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

$array1 = [1, 2, 3, 4, 5];
$array2 = [3, 4, 5, 6, 7];

$result = array_udiff($array1, $array2, 'compareNumbers');

print_r($result);

This finds elements in $array1 not in $array2. The callback uses the spaceship operator for comparison. The result contains values 1 and 2.

Comparing Objects

Compare arrays of objects based on specific object properties.

object_comparison.php

<?php

declare(strict_types=1);

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

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

$products1 = [
    new Product("Laptop", 999.99),
    new Product("Phone", 699.99),
    new Product("Tablet", 399.99)
];

$products2 = [
    new Product("Monitor", 299.99),
    new Product("Keyboard", 99.99),
    new Product("Phone", 699.99)
];

$result = array_udiff($products1, $products2, 'compareProducts');

foreach ($result as $product) {
    echo $product->name . "\n"; 
}

This compares products by price. The callback checks the price property. Products with unique prices in the first array are returned.

Case-Insensitive String Comparison

Perform a case-insensitive comparison of string arrays.

case_insensitive.php

<?php

declare(strict_types=1);

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

$array1 = ["Apple", "Banana", "Cherry"];
$array2 = ["apple", "banana", "grape"];

$result = array_udiff($array1, $array2, 'compareStrings');

print_r($result);

This compares strings ignoring case. The callback uses strcasecmp. Only "Cherry" is different as the others match case-insensitively.

Multi-dimensional Array Comparison

Compare multi-dimensional arrays based on specific elements.

multi_dimensional.php

<?php

declare(strict_types=1);

function compareArrays(array $a, array $b): int {
    return $a['id'] <=> $b['id'];
}

$users1 = [
    ['id' => 1, 'name' => 'Alice'],
    ['id' => 2, 'name' => 'Bob'],
    ['id' => 3, 'name' => 'Charlie']
];

$users2 = [
    ['id' => 2, 'name' => 'Robert'],
    ['id' => 4, 'name' => 'David']
];

$result = array_udiff($users1, $users2, 'compareArrays');

print_r($result); // Outputs users with IDs 1 and 3

This compares arrays by their 'id' elements. The callback checks the id key. Users with unique IDs in the first array are returned.

Multiple Array Comparison

Compare one array against multiple other arrays simultaneously.

multiple_arrays.php

<?php

declare(strict_types=1);

function compareValues($a, $b): int {
    if (is_numeric($a) && is_numeric($b)) {
        return $a <=> $b;
    }
    return strcmp((string)$a, (string)$b);
}

$mainArray = [1, 'apple', 3.14, true, 'orange'];
$array2 = [1, 3.14];
$array3 = ['apple', 'banana'];

$result = array_udiff($mainArray, $array2, $array3, 'compareValues');

print_r($result);

This compares against multiple arrays with mixed types. The callback handles both numeric and string comparisons. Only unique values remain.

Best Practices

Consistent Callbacks: Ensure callbacks return consistent comparison results.
Type Safety: Add type hints to callback parameters when possible.
Performance: For large arrays, optimize callback functions.
Readability: Use descriptive names for callback functions.

Source

PHP array_udiff Documentation

This tutorial covered the PHP array_udiff function with practical examples showing its usage for various comparison scenarios.

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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