CSV x,y -> y,count(y)

gistfile1.hs

import qualified Data.Map.Strict as Map
import Data.Maybe (mapMaybe)
import Text.CSV (parseCSV)
import Text.Printf (printf)

parseFilm (t:y:[]) = Just (t,y)
parseFilm _ = Nothing
 
countYears :: [(String,String)] -> [(String,Int)]
countYears films = Map.toList $ foldl (\m (_,y) -> Map.insertWith (+) y 1 m) Map.empty films

processFilms :: String -> String
processFilms s = unlines . map (uncurry $ printf "%s,%d") $ countYears films
  where films = either (const []) (mapMaybe parseFilm) $ parseCSV "stdin" s

main = interact processFilms