unique elements in a haskell list

Question

okay, this is probably going to be in the prelude, but: is there a standard library function for finding the unique elements in a list? my (re)implementation, for clarificat

Answer 1

Algorithm in Haskell to create a unique list:

data Foo = Foo { id_ :: Int
               , name_ :: String
               } deriving (Show)

alldata = [ Foo 1 "Name"
          , Foo 2 "Name"
          , Foo 3 "Karl"
          , Foo 4 "Karl"
          , Foo 5 "Karl"
          , Foo 7 "Tim"
          , Foo 8 "Tim"
          , Foo 9 "Gaby"
          , Foo 9 "Name"
          ]

isolate :: [Foo] -> [Foo]
isolate [] = []
isolate (x:xs) = (fst f) : isolate (snd f)
  where
    f = foldl helper (x,[]) xs
    helper (a,b) y = if name_ x == name_ y
                     then if id_ x >= id_ y
                          then (x,b)
                          else (y,b)
                     else (a,y:b)

main :: IO ()
main = mapM_ (putStrLn . show) (isolate alldata)

Output:

Foo {id_ = 9, name_ = "Name"}
Foo {id_ = 9, name_ = "Gaby"}
Foo {id_ = 5, name_ = "Karl"}
Foo {id_ = 8, name_ = "Tim"}