On my RSForm, I'd like to set the category ID based on the user group (so if a user belonging to the Joomla Group "Location 1" is viewing the RSForm, I'd like to return only one category ID (the category into which that user group is allowed to submit articles).

How can I do this? I think I need a Hidden Field, but I'm struggling to figure out how to write the case condition to check the user's Joomla Group, and return the appropriate category ID.

SOLVED:
I used this code:

//<code>

$db = JFactory::getDbo();
$user = JFactory::getUser();

//Create a query to grab the group id of the currently logged in user

$db->setQuery("SELECT `group_id` FROM #__user_usergroup_map WHERE `user_id`='". $user->get('id')."'");
$gid = $submissions = $db->loadResult();

//Define the scenario, for example Super User group id = 8 and Registered = 2
if ($gid == 13){ return '71'; }
elseif ($gid == 24){ return '72'; }
elseif ($gid == 22){ return '73'; }
elseif ($gid == 26){ return '14'; }
elseif ($gid == 40){ return '90'; }
elseif ($gid == 25){ return '74'; }
elseif ($gid == 23){ return '75'; }
elseif ($gid == 21){ return '76'; }
//</code>