implemented dropNth

src/Mtlstats/Util.hs

@@ -22,6 +22,7 @@ along with this program.  If not, see <https://www.gnu.org/licenses/>.
 module Mtlstats.Util
   ( nth
   , modifyNth
+  , dropNth
   , updateMap
   , slice
   , capitalizeName
@@ -56,6 +57,18 @@ modifyNth n f = zipWith
   (\i x -> if i == n then f x else x)
   [0..]
 
+-- | Attempt to drop the nth element from a list
+dropNth
+  :: Int
+  -- ^ The index of the element to drop
+  -> [a]
+  -- ^ The list to be modified
+  -> [a]
+  -- ^ The modified list
+dropNth n = foldr
+  (\(i, x) acc -> if i == n then acc else x : acc)
+  [] . zip [0..]
+
 -- | Modify a value indexed by a given key in a map using a default
 -- initial value if not present
 updateMap

test/UtilSpec.hs

@@ -30,6 +30,7 @@ spec :: Spec
 spec = describe "Mtlstats.Util" $ do
   nthSpec
   modifyNthSpec
+  dropNthSpec
   updateMapSpec
   sliceSpec
   capitalizeNameSpec
@@ -64,6 +65,20 @@ modifyNthSpec = describe "modifyNth" $ do
     it "should not modify the value" $
       modifyNth (-1) succ list `shouldBe` [1, 2, 3]
 
+dropNthSpec :: Spec
+dropNthSpec = describe "dropNth" $ mapM_
+
+  (\(label, n, expected) ->
+    context label $
+      it ("should be " ++ show expected) $
+      dropNth n list `shouldBe` expected)
+
+  [ ( "out of bounds", 1, ["foo", "baz"] )
+  , ( "in bounds",     3, list           )
+  ]
+
+  where list = ["foo", "bar", "baz"]
+
 updateMapSpec :: Spec
 updateMapSpec = describe "updateMap" $ do
   let