Richard A. O'Keefe
writes: There are at least four different things that "an Ord version" might mean:
- first sort a list, then eliminate duplicates - sort a list eliminating duplicates stably as you go (think 'merge sort', using 'union' instead of 'merge') - build a balanced tree set as you go - having a list that is already sorted, use that to eliminated duplicates cheaply.
These things have different costs. For example, ...
What I want is more often ordNubBy than ordNub, though.
(ordNubBy you can get via a suitable Ord instance for the element type?) The bigger problem is that you might not have a suitable Ord instance. After all, sets are defined by equality/equivalence relation, not necessarily by Ord. There are many other things you might want to do with a set/collection than just remove duplicates. I notice that Data.Set.map = fromList . (map stuff) . toList That is, build two lists (to be GC'd), as well as the set result. So does the performane cost of from/to List outrun the benefit of Data.Set.union? Depends how much you're mapping vs inserting and checking membership.