31 Jul
2010
31 Jul
'10
3:40 a.m.
On 31 July 2010 06:45, wren ng thornton
Ben wrote:
dear traversable geniuses --
i am looking for "better" implementations of
unzipMap :: M.Map a (b, c) -> (M.Map a b, M.Map a c) unzipMap m = (M.map fst m, M.map snd m)
I don't think you can give a more efficient implementation using the public interface of Data.Map. You need to have a sort of mapping function that allows you to thread them together, either via continuations or via a primitive:
Unless I'm missing something. This one has one traversal... unzipMap :: Ord a => M.Map a (b, c) -> (M.Map a b, M.Map a c) unzipMap = M.foldrWithKey fn (M.empty,M.empty) where fn k a (m1,m2) = (M.insert k (fst a) m1, M.insert k (snd a) m2)