How to compare array keys using array_diff_ukey()

M66 2025-06-06

In PHP, array_diff_ukey() is a very useful function that can be used to compare the differences in key names of two arrays. Unlike the array_diff() function that only compares the values of an array, array_diff_ukey() allows us to compare the keys of an array through a custom comparison function. This function is very suitable for scenarios where multi-dimensional arrays are processed or where key names need to be compared according to complex rules.

grammar

 array_diff_ukey(array $array1, array $array2, callable $key_compare_func): array

Parameter description:

$array1 : The first array.
$array2 : The second array.
$key_compare_func : A callback function that compares two keys. If the return value is less than 0, it means that the key of $array1 is less than the key of $array2 ; if the return value is greater than 0, it means that the key of $array1 is greater than the key of $array2 ; if the return value is equal to 0, it means that the two keys are equal.

Return value:

Returns an array containing the key name and value of elements in $array1 but not in $array2 .

Example

Here is a simple example using array_diff_ukey() to compare the key name differences between two arrays:

 <?php

// The first array
$array1 = [
    'apple' => 100,
    'banana' => 200,
    'orange' => 300,
];

// The second array
$array2 = [
    'banana' => 200,
    'grape' => 400,
    'kiwi' => 500,
];

// Custom key comparison function
function compare_keys($key1, $key2) {
    return strcmp($key1, $key2); // Compare key names using string
}

// use array_diff_ukey Comparison of the differences in key names of two arrays
$result = array_diff_ukey($array1, $array2, 'compare_keys');

// Print results
print_r($result);
?>

Output result:

 Array
(
    [apple] => 100
    [orange] => 300
)

explain

In the above example, the array_diff_ukey() function will compare the key names of the two arrays $array1 and $array2 . In this example, the 'apple' and 'orange' keys in $array1 do not exist in $array2 , so they are retained in the returned result. The 'banana' key is included in both arrays, so it is excluded.

Applicable scenarios

array_diff_ukey() is very suitable for the following scenarios:

Custom comparison of key names : array_diff_ukey() provides powerful functions when you need to compare keys of an array based on custom rules (such as case, character order, etc.).
Processing of multi-dimensional arrays : If your array is multi-dimensional and only needs to compare key names without caring about values, you can use array_diff_ukey() to handle it.

Advanced Application

Suppose we need to compare the keys of two URL arrays and we want to compare the main domain part of the URL. You can extract the main domain name of the URL through the parse_url() function, and then use a custom comparison function to compare.

array_diff_ukey