PHP array_intersect_ukey Function

last modified March 13, 2025

The PHP array_intersect_ukey function computes the intersection of arrays using keys and a user-defined comparison function. It's useful for complex key comparisons.

Basic Definition

The array_intersect_ukey function compares array keys using a callback function. It returns an array containing all entries from the first array whose keys exist in all other arrays.

Syntax: array_intersect_ukey(array $array1, array $array2, ..., callable $key_compare_func): array. The callback should return an integer less than, equal to, or greater than zero.

Basic array_intersect_ukey Example

This shows a simple case-insensitive key comparison between two arrays.

basic_array_intersect_ukey.php

<?php

declare(strict_types=1);

function keyCompare($key1, $key2): int {
    return strcasecmp($key1, $key2);
}

$array1 = ["Name" => "Alice", "Age" => 25];
$array2 = ["name" => "Bob", "City" => "London"];

$result = array_intersect_ukey($array1, $array2, 'keyCompare');

print_r($result);

This compares keys case-insensitively. The callback uses strcasecmp to match "Name" and "name". The result contains matching key-value pairs.

Numeric Key Comparison

Compare numeric keys with a custom tolerance for floating-point differences.

numeric_key_comparison.php

<?php

declare(strict_types=1);

function floatKeyCompare($key1, $key2): int {
    $epsilon = 0.00001;
    $diff = abs($key1 - $key2);
    if ($diff < $epsilon) {
        return 0;
    }
    return ($key1 < $key2) ? -1 : 1;
}

$array1 = [1.00001 => "A", 2.5 => "B"];
$array2 = [1.0 => "X", 2.49999 => "Y"];

$result = array_intersect_ukey($array1, $array2, 'floatKeyCompare');

print_r($result);

This compares floating-point keys with a small tolerance. The callback considers keys equal if they differ by less than 0.00001. Both keys match in this example.

Multi-Array Intersection

Find keys present in three arrays using a custom comparison function.

multi_array_intersection.php

<?php

declare(strict_types=1);

function lengthCompare($key1, $key2): int {
    return strlen($key1) <=> strlen($key2);
}

$array1 = ["apple" => 1, "banana" => 2];
$array2 = ["orange" => 3, "kiwi" => 4];
$array3 = ["pear" => 5, "grape" => 6];

$result = array_intersect_ukey($array1, $array2, $array3, 'lengthCompare');

print_r($result);

This matches keys based on their length. Only "apple" (5 letters) has matching length keys in all arrays ("orange" and "grape"). The callback uses the spaceship operator for comparison.

Object Key Comparison

Compare arrays with object keys using a custom property-based comparison.

object_key_comparison.php

<?php

declare(strict_types=1);

class ProductKey {
    public function __construct(public string $id) {}
}

function productKeyCompare($key1, $key2): int {
    return strcmp($key1->id, $key2->id);
}

$key1 = new ProductKey("P100");
$key2 = new ProductKey("P200");
$key3 = new ProductKey("P100");

$array1 = [$key1 => "Laptop", $key2 => "Phone"];
$array2 = [$key3 => "Tablet"];

$result = array_intersect_ukey($array1, $array2, 'productKeyCompare');

print_r($result);

This compares objects as keys based on their id property. The callback uses strcmp on the id values. Only the P100 key matches between arrays.

Complex Key Matching

Implement advanced key matching with multiple comparison criteria.

complex_key_matching.php

<?php

declare(strict_types=1);

function complexKeyCompare($key1, $key2): int {

    $score = 0;
    $score += strcasecmp(substr($key1, 0, 3), substr($key2, 0, 3));
    $score += (strlen($key1) <=> strlen($key2)) * 2;
    return $score;
}

$array1 = ["user_123" => "Alice", "admin_45" => "Bob"];
$array2 = ["USER_123" => "Active", "guest_78" => "Inactive"];

$result = array_intersect_ukey($array1, $array2, 'complexKeyCompare');

print_r($result);

This implements a multi-factor key comparison. It matches the first 3 characters case-insensitively and considers key length. The "user_123" key matches despite case differences in the second array.

Best Practices

Consistent Returns: Ensure callback always returns integers.
Performance: Keep comparison logic efficient for large arrays.
Type Safety: Add type hints to callback parameters.
Documentation: Clearly document custom comparison rules.

Source

PHP array_intersect_ukey Documentation

This tutorial covered the PHP array_intersect_ukey function with practical examples showing its usage for complex key 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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