PHP array_uintersect_assoc Function

last modified March 13, 2025

The PHP array_uintersect_assoc function computes the intersection of arrays with additional index check, comparing data by a callback function.

Basic Definition

array_uintersect_assoc returns an array containing all values from array1 that are present in all arguments. Keys are used in comparison.

Syntax: array_uintersect_assoc(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_uintersect_assoc Example

This example shows a simple case-insensitive string comparison intersection.

basic_array_uintersect_assoc.php

<?php

declare(strict_types=1);

$array1 = ["a" => "green", "b" => "brown", "c" => "blue"];
$array2 = ["a" => "GREEN", "B" => "yellow", "c" => "BLUE"];

$result = array_uintersect_assoc($array1, $array2, "strcasecmp");

print_r($result);

This compares arrays case-insensitively using strcasecmp. Only elements with matching keys AND case-insensitive values are included.

Custom Object Comparison

Compare arrays of objects using a custom callback function for intersection.

object_comparison.php

<?php

declare(strict_types=1);

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

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

$products2 = [
    "p1" => new Product("Laptop", 899.99),
    "p3" => new Product("Tablet", 399.99)
];

$result = array_uintersect_assoc($products1, $products2, 
    fn($a, $b) => $a->name <=> $b->name);

print_r($result);

This intersects arrays of Product objects comparing only the name property. The same key ("p1") and matching names result in inclusion in the output.

Numeric Comparison with Precision

Compare floating-point numbers with a precision tolerance in the intersection.

float_comparison.php

<?php

declare(strict_types=1);

$array1 = ["a" => 1.2345, "b" => 2.3456, "c" => 3.4567];
$array2 = ["a" => 1.2346, "b" => 2.3450, "d" => 3.4567];

$result = array_uintersect_assoc($array1, $array2, function($a, $b) {
    return abs($a - $b) < 0.001 ? 0 : ($a <=> $b);
});

print_r($result);

This compares floats with 0.001 precision tolerance. Keys must match exactly, while values are considered equal if within the specified tolerance.

Multi-array Intersection

Compute intersection across multiple arrays with custom comparison function.

multi_array_intersection.php

<?php

declare(strict_types=1);

$array1 = ["a" => "apple", "b" => "banana", "c" => "cherry"];
$array2 = ["a" => "APPLE", "c" => "CHERRY", "d" => "date"];
$array3 = ["a" => "Apple", "c" => "Cherry", "e" => "elderberry"];

$result = array_uintersect_assoc($array1, $array2, $array3, "strcasecmp");

print_r($result);

This finds elements present in all three arrays with matching keys and case-insensitive matching values using strcasecmp.

Complex Data Structure Comparison

Compare arrays containing complex data structures with a custom callback.

complex_comparison.php

<?php

declare(strict_types=1);

$array1 = [
    "user1" => ["id" => 1, "name" => "John"],
    "user2" => ["id" => 2, "name" => "Jane"]
];

$array2 = [
    "user1" => ["id" => 1, "name" => "JOHN"],
    "user3" => ["id" => 3, "name" => "Alice"]
];

$result = array_uintersect_assoc($array1, $array2, function($a, $b) {
    return $a["id"] <=> $b["id"];
});

print_r($result);

This intersects arrays of associative arrays comparing only the "id" field. The key "user1" matches and the id values are equal, so it's included.

Best Practices

Consistent Callbacks: Ensure callback returns proper comparison values.
Key Awareness: Remember both keys and values are compared.
Performance: For large arrays, optimize callback functions.
Type Safety: Add type hints in callbacks for robustness.

Source

PHP array_uintersect_assoc Documentation

This tutorial covered the PHP array_uintersect_assoc function with practical examples showing its usage for array intersection 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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