module Reducers (
  leastMostOcc,
  leastMost,
  most,
  least
  ) where

import           Data.List (group, sortBy, sort)
import           Data.Ord  (comparing)

groupOccurrences :: (Ord a) => [a] -> [[a]]
groupOccurrences = sortBy (comparing length) . group . sort

leastMostOcc :: (Ord a) => [a] -> (Int, Int)
leastMostOcc list = ((length . last) occ, (length . head) occ)
  where
    occ = groupOccurrences list

leastMost :: (Ord a) => [a] -> (a, a)
leastMost list = ((head . last) occ, (head . head) occ)
  where
    occ = groupOccurrences list

least :: (Ord a) => [a] -> a
least = fst . leastMost

most :: (Ord a) => [a] -> a
most = snd . leastMost