Sorry to drag this thread out, but here's one more thing you might try... I was thinking, if we just wanted something like intTable :: [Int] -> [(Int, Int)] we could just replace Map with IntMap in the previous solution: intTable xs = IntMap.assocs $! foldl' f IntMap.empty xs where f m x = let m' = IntMap.insertWith (+) x 1 m Just v = IntMap.lookup x m' in v `seq` m' To get another polymorphic version, we could just write this wrapper: freq :: (Enum a) => [a] -> [(a,Int)] freq = map fstToEnum . intTable . map fromEnum where fstToEnum (x,y) = (toEnum x, y) This seems to run faster than the other polymorphic version on my machine. Chad Scherrer Computational Mathematics Group Pacific Northwest National Laboratory "Time flies like an arrow; fruit flies like a banana." -- Groucho Marx