how to put dynamic info in an array?

[eluser]dadamssg[/eluser]
Im trying to put dynamic info in an array. Im setting a session variable to hold which page the user is on so if they login they will be redirected to the page they were on...this isn't working

Code:

$eventid = $row->eventid;
        $newdata = array(
                   'page'  => "event/index/$eventid",
               );
        $this->session->set_userdata($newdata);