[development] Creating a custom filter without real field

I need to filter repeated fields (not nid, so distinct don't work) in some views. I found how to make it using hook_views_pre_render(&$view). I want to make a module to "tag" displays that must be filtered. To do so I have created a filter; where you choose which fields should be unique. Then I am trying to use hook_pre_render() to eliminate the results; but in $vews->result there are fields alias, and I just have fields id. How can I translate field id to field alias? Thanks. (I can post code if needed) -- *La vida no ha de ser feliç, ha de ser plena. *Abans d'imprimir aquest missatge, pensa en el medi ambient.