Hello, I need to calculate the frequency of each character in a String. And if I can do this really well in C, I don't find a nice (and fast) answer in haskell. I tried several functions, listed below, and even the fastest do a lot of unnecessary things :

A while back, I was trying to build a "table" function similar to what you describe, and Dean Herrington helped me speed it up and stop the stack overflows I had been getting. Here it is, in case this is useful to you... table :: (Ord a) => [a] -> [(a,Int)] table xs = Map.assocs $! foldl' f Map.empty xs where f m x = let m' = Map.insertWith (+) x 1 m Just v = Map.lookup x m' in v `seq` m' I would be interested in whether this is much slower than the other approaches you've tried. If a faster approach could be made polymorphic, I'd have a faster way to build tables! Chad Scherrer Computational Mathematics Group Pacific Northwest National Laboratory "Time flies like an arrow; fruit flies like a banana." -- Groucho Marx