Use array_diff_key() to quickly remove blacklist key names

M66 2025-06-06

In PHP, we often need to delete specific keys from an array based on certain conditions. PHP provides a variety of ways to manipulate arrays, where the array_diff_key() function is very suitable for removing certain keys from an array.

In this article, we will explain how to use the array_diff_key() function, combined with the blacklisting mechanism to quickly remove specified keys from an array.

What is the array_diff_key() function?

array_diff_key() is a PHP built-in function that compares the keys of two arrays and returns elements corresponding to those keys that are not in the second array. That is to say, using array_diff_key() can filter out keys in the second array.

Function prototype:

 array array_diff_key ( array $array1 , array $array2 )

$array1 : The first array.
$array2 : The second array, used to compare keys.

The function returns a new array containing the keys in $array1 and not the keys in $array2 .

Use scenario: Remove the blacklist key from the array

Suppose we have an array of user information, we need to quickly remove some unwanted key names based on a blacklist array. For example, we have an array containing user information, which may have sensitive data (such as passwords), and we want to remove this sensitive information through a blacklist array.

Sample code:

 <?php

// Original user data
$user_data = [
    'username' => 'john_doe',
    'email' => 'john@example.com',
    'password' => 'secret_password',
    'phone' => '123-456-7890',
    'address' => '123 Main St, Anytown, USA',
    'url' => 'https://m66.net/profile/john_doe'
];

// Blacklist array，Contains the key name we want to remove
$blacklist = [
    'password' => null,
    'url' => null
];

// use array_diff_key Remove keys from the blacklist
$filtered_data = array_diff_key($user_data, $blacklist);

// Output the result after processing
print_r($filtered_data);
?>

Output result:

 Array
(
    [username] => john_doe
    [email] => john@example.com
    [phone] => 123-456-7890
    [address] => 123 Main St, Anytown, USA
)

Code parsing:

$user_data : contains various user information, including username, email, password, phone number, address and a URL.
$blacklist : This is an array containing blacklist key names. We specify the 'password' and 'url' keys in the blacklist array, which are removed from the original array.
array_diff_key($user_data, $blacklist) : This line of code will return a new array, where only the keys in $user_data that are not in the blacklist array $blacklist are retained. The final returned array is the data after removing sensitive information.

This way, you can quickly and flexibly remove specified keys from any array, especially when processing user information, which can help you effectively block sensitive data.

Why choose array_diff_key() ?

The array_diff_key() function is an ideal choice for handling such requirements, and it is very efficient because it directly compares the keys of the array, not the values of the array. Compared with other ways that require traversing arrays one by one, array_diff_key() can filter out unnecessary keys through one comparison, saving processing time, especially for larger data sets.

Conclusion

Operating arrays in PHP is a common task in daily development. Mastering some commonly used array functions can greatly improve work efficiency. Using array_diff_key() to quickly remove blacklist keys is an efficient and easy-to-implement approach. If you have multiple keys that need to be deleted, array_diff_key() provides an elegant solution.

Hope this article can help you understand how to use the array_diff_key() function to handle key filtering problems in arrays. If you have any other questions, feel free to ask!

array_diff_key