How to get an array of specific "key" in multidimensional array without looping

PHP 5.5+

Starting PHP5.5+ you have array_column() available to you, which makes all of the below obsolete.

PHP 5.3+

$ids = array_map(function ($ar) {return $ar['id'];}, $users);

Solution by @phihag will work flawlessly in PHP starting from PHP 5.3.0, if you need support before that, you will need to copy that wp_list_pluck.

PHP < 5.3

Wordpress 3.1+

In Wordpress there is a function called wp_list_pluck If you're using Wordpress that solves your problem.

PHP < 5.3

If you're not using Wordpress, since the code is open source you can copy paste the code in your project (and rename the function to something you prefer, like array_pick). View source here

Since PHP 5.5, you can use array_column:

$ids = array_column($users, 'id');

This is the preferred option on any modern project. However, if you must support PHP<5.5, the following alternatives exist:

Since PHP 5.3, you can use array_map with an anonymous function, like this:

$ids = array_map(function ($ar) {return $ar['id'];}, $users);

Before ^{_{(Technically PHP 4.0.6+)}}, you must create an anonymous function with create_function instead:

$ids = array_map(create_function('$ar', 'return $ar["id"];'), $users);

If id is the first key in the array, this'll do:

$ids = array_map('current', $users);

You should not necessarily rely on this though. :)