Useful Joomla snips

Joomla.php

<?php 

// Change Joomla user groups programatically

jimport('joomla.user.helper'); 
JUserHelper::removeUserFromGroup($user_id, $group_id);
JUserHelper::addUserToGroup($user_id, $group_id);

// Get a user's view levels

$user  =& JFactory::getUser();
$aid = max ($user->getAuthorisedViewLevels());

// Programatically login a Joomla user

$mainframe->login(array('username'=>$_POST['username'], 'password'=>$_POST['password']), array('silent'=>true))

?>