advanced patterns with PHP's array_map when processing associative arrays with nested structures
I'm maintaining legacy code that I'm having trouble with Quick question that's been bugging me - This might be a silly question, but I'm working with an scenario with PHP's `array_map` function when attempting to process an associative array that contains nested structures. I'm using PHP 8.1 and trying to transform an array of user data, where each user has a nested array of preferences. Here’s the code I'm working with: ```php $users = [ [ 'name' => 'Alice', 'preferences' => [ 'theme' => 'dark', 'notifications' => true ] ], [ 'name' => 'Bob', 'preferences' => [ 'theme' => 'light', 'notifications' => false ] ] ]; $transformedUsers = array_map(function($user) { return [ 'username' => $user['name'], 'prefersDarkTheme' => $user['preferences']['theme'] === 'dark', ]; }, $users); print_r($transformedUsers); ``` Running this code, I expect to get an array that simply indicates whether each user prefers a dark theme, but I'm getting an behavior: `Notice: Undefined index: preferences in ...`. After some debugging, I realized that this behavior occurs if any user does not have the `preferences` key. To handle cases where some users might not have this key, I've tried using the null coalescing operator like so: ```php $transformedUsers = array_map(function($user) { return [ 'username' => $user['name'], 'prefersDarkTheme' => ($user['preferences']['theme'] ?? 'light') === 'dark', ]; }, $users); ``` However, even with this adjustment, I still receive the same notice if I pass an incomplete user data structure. What is the best practice to ensure my code gracefully handles missing keys in associative arrays without throwing notices? I've considered adding checks before accessing the nested arrays, but I'm concerned about code readability and maintainability. Any suggestions? This is part of a larger service I'm building. Thanks in advance! My development environment is Windows. Any help would be greatly appreciated! Any ideas what could be causing this? For context: I'm using Php on Ubuntu 22.04. Hoping someone can shed some light on this.