Merge pull request #575 from kostya/group_by

# enumerable#group_by

lib-topaz/enumerable.rb

@@ -253,4 +253,15 @@ def none?(&block)
     end
     true
   end
+
+  def group_by(&block)
+    return self.enum_for(:group_by) unless block
+    h = {}
+    self.each do |e|
+      v = yield e
+      a = h.fetch(v) { |v| h[v] = [] }
+      a << e
+    end
+    h
+  end
 end

spec/tags/core/enumerable/group_by_tags.txt

@@ -1,4 +1 @@
-fails:Enumerable#group_by returns a hash with values grouped according to the block
-fails:Enumerable#group_by returns an empty hash for empty enumerables
-fails:Enumerable#group_by returns an Enumerator if called without a block
 fails:Enumerable#group_by gathers whole arrays as elements when each yields multiple