Wordpress: get users by role

Here's a little function I cooked up to fetch users by their roles.

Written by Daniel, April 4, 2010

I needed a simple way to get all users by their roles, and none of WP’s built in functions seemed to be able to do this.

	public function get_users_by_role($role = 'all')
	{
		global $wpdb;
		$query = $wpdb -> prepare("SELECT {$wpdb -> users}.ID as `id`, {$wpdb -> usermeta}.meta_value as `capabilities` FROM {$wpdb -> users} JOIN {$wpdb -> usermeta} ON {$wpdb -> users}.ID = {$wpdb -> usermeta}.user_id WHERE {$wpdb -> usermeta}.meta_key = 'wp_capabilities'");
		$userdata = $wpdb -> get_results($query);
		$users = Array();
		foreach($userdata as $data)
		{
			$caps = unserialize($data -> capabilities);
			if($caps[$role] == true || $role == 'all')
			{
				$users[] = get_userdata($data -> id);
			}
		}
		return $users;
	}

There’s a pretty long query in there which pretty much just selects the ID from the wp_users table and the wp_capabilities value from the wp_usermeta table.

Then there’s a loop which checks that the selected user id has the wanted role, and then an array of all users with their data is returned. Pretty simple.

Use it like this:

$admins = get_users_by_role('administrator');
foreach($admins as $admin)
{
	echo $admin -> user_nicename . '<br />';
}

Outputs something like:
admin
admin2

If anyone knows of a simpler way of doing this, please let me know.