use Ord for nub

addresses purescript#91

O(n*logn)

Author: matthewleon

src/Data/Array.purs

@@ -117,17 +117,18 @@ import Prelude
 import Control.Alt ((<|>))
 import Control.Alternative (class Alternative)
 import Control.Lazy (class Lazy, defer)
+import Control.Monad.Eff (foreachE)
 import Control.Monad.Rec.Class (class MonadRec, Step(..), tailRecM2)
 import Control.Monad.ST (pureST)
-import Data.Array.ST (unsafeFreeze, emptySTArray, pokeSTArray, pushSTArray, modifySTArray, withArray)
+import Data.Array.ST (unsafeFreeze, unsafeThaw, emptySTArray, pokeSTArray, pushSTArray, modifySTArray, withArray)
 import Data.Array.ST.Iterator (iterator, iterate, pushWhile)
 import Data.Foldable (class Foldable, foldl, foldr, traverse_)
 import Data.Foldable (foldl, foldr, foldMap, fold, intercalate, elem, notElem, find, findMap, any, all) as Exports
 import Data.Maybe (Maybe(..), maybe, isJust, fromJust)
 import Data.NonEmpty (NonEmpty, (:|))
 import Data.Traversable (scanl, scanr) as Exports
 import Data.Traversable (sequence, traverse)
-import Data.Tuple (Tuple(..), uncurry)
+import Data.Tuple (Tuple(..), fst, snd, uncurry)
 import Data.Unfoldable (class Unfoldable, unfoldr)
 import Partial.Unsafe (unsafePartial)
 
@@ -873,8 +874,19 @@ groupBy op xs =
 -- | nub [1, 2, 1, 3, 3] = [1, 2, 3]
 -- | ```
 -- |
-nub :: forall a. Eq a => Array a -> Array a
-nub = nubBy eq
+nub :: forall a. Ord a => Array a -> Array a
+nub arr = case head indexedAndSorted of
+  Nothing -> []
+  Just x -> map fst $ sortWith snd $ pureST do
+     -- TODO: use NonEmptyArrays here to avoid partial functions
+     result <- unsafeThaw $ singleton x
+     foreachE indexedAndSorted \pair@(Tuple x' i) -> do
+       lst <- fst <<< unsafePartial (fromJust <<< last) <$> unsafeFreeze result
+       when (lst /= x') $ void $ pushSTArray result pair
+     unsafeFreeze result
+
+  where
+  indexedAndSorted = sort $ mapWithIndex (flip Tuple) arr
 
 -- | Remove the duplicates from an array, where element equality is determined
 -- | by the specified equivalence relation, creating a new array.

test/Test/Data/Array.purs

@@ -313,6 +313,9 @@ testArray = do
   log "nub should remove duplicate elements from the list, keeping the first occurence"
   assert $ A.nub [1, 2, 2, 3, 4, 1] == [1, 2, 3, 4]
 
+  log "nub should preserve order"
+  assert $ A.nub [1, 3, 4, 2, 2, 1] == [1, 3, 4, 2]
+
   log "nubBy should remove duplicate items from the list using a supplied predicate"
   let nubPred = \x y -> if odd x then false else x == y
   assert $ A.nubBy nubPred [1, 2, 2, 3, 3, 4, 4, 1] == [1, 2, 3, 3, 4, 1]