Optimize HashDict.take and HashDict.split, update CHANGELOG

Author: José Valim

CHANGELOG.md

@@ -6,7 +6,7 @@
   * [IEx] Support `ls` with colored output
   * [Kernel] Add `Enum.at`, `Enum.fetch` and `Enum.fetch!`
   * [Kernel] Add `String.to_integer` and `String.to_float`
-  * [Kernel] Add `Dict.pop` and `Dict.fetch!`
+  * [Kernel] Add `Dict.take`, `Dict.drop`, `Dict.split`, `Dict.pop` and `Dict.fetch!`
   * [Kernel] Many optimizations for code compilation
   * [Kernel] `in` can be used with right side expression outside guards
   * [Kernel] Add `Node.get_cookie/0` and `Node.set_cookie/2`

lib/elixir/lib/dict.ex

@@ -367,14 +367,13 @@ defmodule Dict do
   end
 
   @doc """
-  
-  Returns a tuple of two dicts, where the first dict contains only 
-  entries from `dict` with keys in `keys`, and the second dict 
+  Returns a tuple of two dicts, where the first dict contains only
+  entries from `dict` with keys in `keys`, and the second dict
   contains only entries from `dict` with keys not in `keys`
- 
+
   Any non-member keys are ignored.
 
-  ## Examples 
+  ## Examples
 
       iex> d = HashDict.new([a: 1, b: 2])
       ...> { d1, d2 } = Dict.split(d, [:a, :c])
@@ -398,11 +397,10 @@ defmodule Dict do
   end
 
   @doc """
-  
   Returns a new dict where the the given `keys` a removed from `dict`.
   Any non-member keys are ignored.
 
-  ## Examples 
+  ## Examples
 
       iex> d = HashDict.new([a: 1, b: 2])
       ...> d = Dict.drop(d, [:a, :c, :d])
@@ -421,11 +419,10 @@ defmodule Dict do
   end
 
   @doc """
-  
   Returns a new dict where only the keys in `keys` from `dict` are
   included. Any non-member keys are ignored.
 
-  ## Examples 
+  ## Examples
 
       iex> d = HashDict.new([a: 1, b: 2])
       ...> d = Dict.take(d, [:a, :c, :d])
@@ -441,7 +438,7 @@ defmodule Dict do
   @spec take(t, keys) :: t
   def take(dict, keys) do
     target(dict).take(dict, keys)
-  end  
+  end
 
   @doc """
   Returns an empty dict of the same type as `dict`.

lib/elixir/lib/hash_dict.ex

@@ -292,32 +292,35 @@ defmodule HashDict do
   and another containing entries with key not in keys.
   Returns a 2-tuple of the new dicts.
   """
-  def split(dict, keys) when keys == [] do
-    { new(), dict }
+  def split(dict, keys) do
+    split(keys, new, dict)
   end
 
-  def split(dict, keys) do
-    acc = { new(), new() }
-    dict_fold dict, acc, fn({ k, v }, { take, drop }) ->
-      if Enum.member?(keys, k) do
-        { put(take, k, v), drop }
-      else
-        { take, put(drop, k, v) }
-      end
+  defp split([], including, excluding) do
+    { including, excluding }
+  end
+
+  defp split([key|keys], including, excluding) do
+    case dict_delete(excluding, key) do
+      { excluding, _, 0 } -> split(keys, including, excluding)
+      { excluding, value, _ } -> split(keys, put(including, key, value), excluding)
     end
   end
 
   @doc """
   Returns a new dict with only the entries
-  which key is in keys
+  which key is in keys.
   """
-  def take(_, keys) when keys == [] do
-    new()
+  def take(dict, keys) do
+    take(dict, keys, new)
   end
 
-  def take(dict, keys) do
-    { members, _ } = split(dict, keys)
-    members
+  defp take(_dict, [], acc), do: acc
+  defp take(dict, [key|keys], acc) do
+    case fetch(dict, key) do
+      { :ok, value } -> take(dict, keys, put(acc, key, value))
+      :error -> take(dict, keys, acc)
+    end
   end
 
   @doc """

lib/elixir/lib/list_dict.ex

@@ -146,14 +146,10 @@ defmodule ListDict do
   and another containing entries with key not in keys.
   Returns a 2-tuple of the new dicts.
   """
-  def split(dict, keys) when keys == [] do
-    { new(), dict }
-  end
-
   def split(dict, keys) do
     acc = { new(), new() }
     Enum.reduce dict, acc, fn({ k, v }, { take, drop }) ->
-      if Enum.member?(keys, k) do
+      if :lists.member(k, keys) do
         { [{k,v}|take], drop }
       else
         { take, [{k,v}|drop] }