Paul Moore <p.f.mo...@gmail.com> writes: > How would I efficiently write a function in Haskell to count > occurrences of unique elements in a (potentially very large) list? For > example, given the list [1,2,3,4,5,3,4,2,4] I would like the output > [[1,1], [2,2], [3,2], [4,3], [5,1]] (or some equivalent > representation).
import qualified Data.Map as Map import Data.Map (Map) histogram :: Ord a => [a] -> [(a,Int)] histogram = Map.assocs . foldl f Map.empty where f m k = Map.insertWith (+) k 1 m G. -- Gregory Collins <g...@gregorycollins.net> _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe