Magnus Jonsson wrote:
Dear Haskell Cafe,
When programming the other day I ran into this problem. What I want to
do is a function that would work like this:
splitStreams::Ord a=>[(a,b)]->[(a,[b])]
splitStreams [(3,x),(1,y),(3,z),(2,w)]
[(3,[x,z]),(1,[y]),(2,[w])]
A O(n log(n)) algorithm is easy if you use Data.Map:
> import qualified Data.Map as Map
>
> splitStreamsMap :: Ord a => [(a,b)] -> Map.Map a [b]
> splitStreamsMap = foldl add Map.empty
> where add (a,b) m = Map.insertWith (++) a [b]
>
> splitStreams = Map.fromList . splitStreamsMap
Twan
_______________________________________________
Haskell-Cafe mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/haskell-cafe
