nDCG in Haskell. Additionally, I draw graphs and serialize to csv (using Chart and Cassava).

Lib.hs

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE DeriveGeneric #-}
module Lib
    ( writeNDCGs
    , serializeNDCG
    ) where
import Data.List
import Graphics.Rendering.Chart.Easy
import Graphics.Rendering.Chart.Backend.Diagrams
import Control.Lens

import GHC.Generics
import qualified Data.Csv as DC

cg :: [Double] -> [Double]
cg gx = unfoldr consCG (0.0, gx)
  where
    consCG (_, []) = Nothing
    consCG (m, h:t) = Just (m + h, (m + h, t))

dcg :: [Double] -> [Double]
dcg (h : tgx) = h : unfoldr consDCG (2, h, tgx)
  where
    l2 x = logBase 2 x
    consDCG (_, _, []) = Nothing
    consDCG (i, m, h:t) =
      let term = m + h / l2 i in
        Just (term, (succ i, term, t))

icg :: [Double] -> [Double]
icg gx = sortBy (flip $ compare) gx

ndcg :: [Double] -> [Double]
ndcg gx = map (\(a,b) -> a/b) $ zip (dcg gx) (dcg . icg $ gx)

writeNDCGs :: Foldable t => t [Double] -> IO ()
writeNDCGs gxs = toFile def{_fo_format=SVG} "example.svg" $ do
  layout_title .= "Comparison between Google and Bing"
  layout_x_axis . laxis_title .= "Rank (Top20)"
  layout_y_axis . laxis_title .= "nDCG"
  mapM_ (plot . line "Google" . (: []) . zip [0.0 :: Double ..] . ndcg) gxs
  -- plot (line "Bing"   [zip [0.0 :: Double ..] (ndcg gB)])

data CsvNDCG = CsvNDCG
  { _rank      :: !Int
  , _symbolRel :: !String
  , _cg        :: !Int
  , _dcg       :: !Double
  } deriving Generic

-- instance DC.FromNamedRecord CsvNDCG
instance DC.ToNamedRecord   CsvNDCG
instance DC.DefaultOrdered  CsvNDCG

relToSymbol 0 = "×"
relToSymbol 1 = "△"
relToSymbol 2 = "○"
relToSymbol 3 = "◎"

serializeNDCG gx = DC.encodeDefaultOrderedByName $ zipWith4 CsvNDCG [1..] syms lcg lndcg
  where
    syms  = map relToSymbol gx
    lcg   = map round $ cg gx
    lndcg = dcg gx

Main.hs

module Main where

import Lib
import qualified Data.ByteString.Lazy as BL

-- There are results of searching by some kind of query and evaluating it in four levels.
gGoogle = [3,1,3,3,3,3,0,2,2,1,1,0,0,1,1,1,3,0,1,1]
gBing   = [3,3,1,0,0,3,3,0,2,0,0,1,0,3,2,0,3,0,0,0]

main :: IO ()
main = do
  writeNDCGs [gGoogle, gBing]
  BL.writeFile "./ndcg.csv" (BL.concat $ map serializeNDCG [gGoogle, gBing])