PHP array_diff_ukey Function

last modified March 13, 2025

The PHP array_diff_ukey function compares array keys using a callback function. It returns the difference between arrays based on key comparison.

Basic Definition

The array_diff_ukey function computes the difference of arrays using keys. It compares keys with a user-supplied callback function.

Syntax: array_diff_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_diff_ukey Example

This example shows simple key comparison between two arrays using a callback.

basic_array_diff_ukey.php

<?php

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

$array1 = ['a' => 1, 'b' => 2, 'c' => 3];
$array2 = ['A' => 4, 'B' => 5];

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

print_r($result);

The callback performs case-insensitive comparison. Only key 'c' exists in $array1 but not in $array2 when ignoring case.

Comparing Numeric Keys

This example demonstrates comparing numeric keys with custom logic.

numeric_keys.php

<?php

function numericCompare($key1, $key2) {
    return $key1 <=> $key2;
}

$array1 = [10 => 'a', 20 => 'b', 30 => 'c'];
$array2 = [15 => 'd', 20 => 'e'];

$result = array_diff_ukey($array1, $array2, 'numericCompare');

print_r($result);

The callback uses the spaceship operator for numeric comparison. Keys 10 and 30 exist only in the first array, so they appear in the result.

Multiple Array Comparison

Compare one array against multiple arrays with custom key comparison.

multiple_arrays.php

<?php

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

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

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

print_r($result);

The callback compares keys by length. Only 'banana' and 'cherry' have unique lengths not found in other arrays.

Object Key Comparison

Compare arrays with object keys using a custom comparison function.

object_keys.php

<?php

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

function productCompare($key1, $key2) {
    return strcmp($key1->id, $key2->id);
}

$key1 = new ProductKey('p1');
$key2 = new ProductKey('p2');
$key3 = new ProductKey('p3');

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

$result = array_diff_ukey($array1, $array2, 'productCompare');

print_r($result);

The callback compares object properties. Both keys in $array1 are different from $array2's key based on their id property values.

Case-Sensitive String Comparison

Perform case-sensitive key comparison between arrays.

case_sensitive.php

<?php

function caseSensitiveCompare($key1, $key2) {
    return strcmp($key1, $key2);
}

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

$result = array_diff_ukey($array1, $array2, 'caseSensitiveCompare');

print_r($result);

The callback performs case-sensitive comparison. All keys differ due to different casing, so all elements from $array1 are returned.

Best Practices

Consistent Callbacks: Ensure your callback returns consistent comparison results.
Type Safety: Add type hints to callback parameters when possible.
Performance: Use simple comparison logic for large arrays.
Readability: Name callback functions descriptively.

Source

PHP array_diff_ukey Documentation

This tutorial covered the PHP array_diff_ukey function with practical examples showing its usage for various 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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