I have read a few discussions on Unique filter - lookup then roll up. But i really can't seem to figure it out. 

I have my calendar synced - then I have a column of attendees, which is linked to companies. So each row has the different company in the email, but obviously , it can have the same company more than once, given you can have several people from one company. 

i need to create a column to get the unique values here of this column, but unique filter does not work. Please need your help.