Im a bit lost on how to approach this. I have a list of purchase order confirmations and I want to return a "this one" for each where the trailing text is max:

P0001-1
P0001-2 this one
P0002-1 this one
P0003-1 this one
P0004-1 this one
P0005-1
P0005-2 this one

The formula needs to be automatic (im currently using remove duplicates functionality)
Any ideas would be appreciated.