Frequency.hs

-- file:HuffmanEncoding/Frequency.hs
module Frequency where

import Data.List(nub,foldl')

frequencies :: (Eq a) => [a] -> [(a, Double)]
frequencies s = zip (nub s) (map divide qset)
            where divide (_,d) = (d / (total qset))
                  qset = quantities (nub s) s

total :: [(a,Double)] -> Double 
total xs = foldl' step 0 xs
    where step acc (_,d) = acc + d

quantities :: (Eq a) => [a] -> [a] -> [(a, Double)]
quantities ls xs = foldr ((:) . step) [] ls
    where step l = (l, quantity l xs)

quantity :: (Eq a) => a -> [a] -> Double 
quantity s xs  = foldl' step 0 xs
    where step acc x | x == s    = 1 + acc
                     | otherwise = acc