filter duplicates
 

Hoping someone can help, I have a filter list that contains duplicates. I
have set up the advanced filter and have applied the filter
countif($A$2:$a$1000,A2)1
but it doesn't seem to work. I think the logic is correct as I have tried
it on a conditional format and that works fine.

Can I do what I'm trying to do? I DON'T want to delete the duplicates, I
want to keep them! In preference I want to lose the unique records.

Any ideas?