General Support: editing sql that lists collections

I am wondering how I can do a if statment in the plog-functons.php page

What I am wanting to do is at the top of the file have
$roleid = $_GET['r'];
and then on line I need to do the below

[php]
if($roleid =='14'){
$sql = "SELECT * FROM `".PLOGGER_TABLE_PREFIX."collections`".$where."AND supervisors_only='y'".$order.$limit;
}else{
$sql = "SELECT * FROM `".PLOGGER_TABLE_PREFIX."collections`".$where."AND supervisors_only='n'".$order.$limit;
}
[/php]

my issue is when I do the above I get a Undefined variable: roleid error
so it seems like the $_GET['r']; is not working even though I have a value in the address bar?
my addressbar looks like this
http://www.mydomain.com/photogallery/index.php?r=14
thanks