Ranking methods: Difference between revisions

=={{header|Haskell}}==

<lang Haskell>

import Data.List (groupBy, sort, intercalate)

type Item = (Int, String)

type ItemList = [Item]

type ItemGroups = [ItemList]

type RankItem a = (a, Int, String)

type RankItemList a = [RankItem a]

-- make sure the input is ordered and grouped by score

prepare :: ItemList -> ItemGroups

prepare = groupBy gf . reverse . sort

where gf (a, _) (b, _) = a == b

-- give an item a rank

rank :: Num a => a -> Item -> RankItem a

rank n (a, b) = (n, a, b)

-- ranking methods

standard, modified, dense, ordinal :: ItemGroups -> RankItemList Int

standard = ms 1 where

ms _ [] = []

ms n (x:xs) = map (rank n) x ++ ms (n + length x) xs

modified = md 1 where

md _ [] = []

md n (x:xs) = let l = length x

nl = n + l

nl1 = nl - 1

in map (rank nl1) x ++ md (n + l) xs

dense = md 1 where

md _ [] = []

md n (x:xs) = map (rank n) x ++ md (n + 1) xs

ordinal = zipWith rank [1..] . concat

fractional :: ItemGroups -> RankItemList Double

fractional = mf 1.0 where

mf _ [] = []

mf n (x:xs) = let l = length x

o = take l [n ..]

ld = fromIntegral l

a = sum o / ld

in map (rank a) x ++ mf (n + ld) xs

-- sample data

test :: ItemGroups

test = prepare

[ (44, "Solomon")

, (42, "Jason")

, (42, "Errol")

, (41, "Garry")

, (41, "Bernard")

, (41, "Barry")

, (39, "Stephen") ]

-- print rank items nicely

nicePrint :: Show a => String -> RankItemList a -> IO ()

nicePrint xs items = do

putStrLn xs

mapM_ np items

putStr "\n"

where np (a, b, c) = putStrLn $ intercalate "\t" [show a, show b, c]

main :: IO ()

main = do

nicePrint "Standard:" $ standard test

nicePrint "Modified:" $ modified test

nicePrint "Dense:" $ dense test

nicePrint "Ordinal:" $ ordinal test

nicePrint "Fractional:" $ fractional test

</lang>

Output:

<pre>

Standard:

1 44 Solomon

2 42 Jason

2 42 Errol

4 41 Garry

4 41 Bernard

4 41 Barry

7 39 Stephen

Modified:

1 44 Solomon

3 42 Jason

3 42 Errol

6 41 Garry

6 41 Bernard

6 41 Barry

7 39 Stephen

Dense:

1 44 Solomon

2 42 Jason

2 42 Errol

3 41 Garry

3 41 Bernard

3 41 Barry

4 39 Stephen

Ordinal:

1 44 Solomon

2 42 Jason

3 42 Errol

4 41 Garry

5 41 Bernard

6 41 Barry

7 39 Stephen

Fractional:

1.0 44 Solomon

2.5 42 Jason

2.5 42 Errol

5.0 41 Garry

5.0 41 Bernard

5.0 41 Barry

7.0 39 Stephen

</pre>