This is the query we use to load in ALLCATEGORIES
$db = JFactory::getDbo();
$arr_catids = array();
$catsql = "SELECT cat.id, cat.title as name, cat.params FROM #__categories as cat WHERE cat.extension='com_jevents' ";
$db->setQuery($catsql);
$allcat_catids = $db->loadObjectList('id');
$db = JFactory::getDbo();
$db->setQuery("Select catid from #__jevents_catmap WHERE evid = " . $event->ev_id());
$allcat_eventcats = $db->loadColumn();
$allcats = array();
foreach ($allcat_eventcats as $catid)
{
if (isset($allcat_catids[$catid]))
{
$allcats[] = $allcat_catids[$catid]->name;
}
}
$categories = implode(", ", $allcats);
$categories should then output a comma seperated list.