Merge pull request #68 from damncabbage/topic/mapWithIndex

Adds mapWithIndex (map with a generated index)

Author: garyb

src/Data/Array.purs

@@ -68,6 +68,7 @@ module Data.Array
   , filterM
   , mapMaybe
   , catMaybes
+  , mapWithIndex
 
   , sort
   , sortBy
@@ -411,6 +412,14 @@ mapMaybe f = concatMap (maybe [] singleton <<< f)
 catMaybes :: forall a. Array (Maybe a) -> Array a
 catMaybes = mapMaybe id
 
+-- | Apply a function to each element in an array, supplying a generated
+-- | zero-based index integer along with the element, creating an array
+-- | with the new elements.
+mapWithIndex :: forall a b. (Int -> a -> b) -> Array a -> Array b
+mapWithIndex f xs =
+  zipWith f (range 0 (length xs - 1)) xs
+
+
 --------------------------------------------------------------------------------
 -- Sorting ---------------------------------------------------------------------
 --------------------------------------------------------------------------------

test/Test/Data/Array.purs

@@ -5,7 +5,7 @@ import Prelude
 import Control.Monad.Eff (Eff)
 import Control.Monad.Eff.Console (log, CONSOLE)
 
-import Data.Array (range, foldM, unzip, zip, zipWithA, zipWith, intersectBy, intersect, (\\), deleteBy, delete, unionBy, union, nubBy, nub, groupBy, group', group, span, dropWhile, drop, takeWhile, take, sortBy, sort, catMaybes, mapMaybe, filterM, filter, concat, concatMap, reverse, alterAt, modifyAt, updateAt, deleteAt, insertAt, findLastIndex, findIndex, elemLastIndex, elemIndex, (!!), uncons, init, tail, last, head, insertBy, insert, snoc, (:), length, null, singleton, fromFoldable)
+import Data.Array (range, foldM, unzip, zip, zipWithA, zipWith, intersectBy, intersect, (\\), deleteBy, delete, unionBy, union, nubBy, nub, groupBy, group', group, span, dropWhile, drop, takeWhile, take, sortBy, sort, catMaybes, mapMaybe, mapWithIndex, filterM, filter, concat, concatMap, reverse, alterAt, modifyAt, updateAt, deleteAt, insertAt, findLastIndex, findIndex, elemLastIndex, elemIndex, (!!), uncons, init, tail, last, head, insertBy, insert, snoc, (:), length, null, singleton, fromFoldable)
 import Data.Foldable (for_, foldMapDefaultR, class Foldable, all)
 import Data.Maybe (Maybe(..), isNothing, fromJust)
 import Data.Tuple (Tuple(..))
@@ -201,6 +201,9 @@ testArray = do
   log "catMaybe should take an array of Maybe values and throw out Nothings"
   assert $ catMaybes [Nothing, Just 2, Nothing, Just 4] == [2, 4]
 
+  log "mapWithIndex applies a function with an index for every element"
+  assert $ mapWithIndex (\i x -> x - i) [9,8,7,6,5] == [9,7,5,3,1]
+
   log "sort should reorder a list into ascending order based on the result of compare"
   assert $ sort [1, 3, 2, 5, 6, 4] == [1, 2, 3, 4, 5, 6]