Changed the implementation of Enumerable#group_by to use a double arr…

…ay approach instead of a hash such that the insert order is honored [DHH/Marcel]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@8516 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activesupport/CHANGELOG

@@ -1,5 +1,7 @@
 *SVN*
 
+* Changed the implementation of Enumerable#group_by to use a double array approach instead of a hash such that the insert order is honored [DHH/Marcel]
+
 * remove multiple enumerations from ActiveSupport::JSON#convert_json_to_yaml when dealing with date/time values.  [rick]
 
 * Hash#symbolize_keys skips keys that can't be symbolized.  #10500 [Brad Greenlee]

activesupport/lib/active_support/core_ext/enumerable.rb

@@ -15,8 +15,13 @@ module Enumerable
   #   "2006-02-24 -> Transcript, Transcript"
   #   "2006-02-23 -> Transcript"
   def group_by
-    inject({}) do |groups, element|
-      (groups[yield(element)] ||= []) << element
+    inject([]) do |groups, element|
+      value = yield(element)
+      if (last_group = groups.last) && last_group.first == value
+        last_group.last << element
+      else
+        groups << [value, [element]]
+      end
       groups
     end
   end if RUBY_VERSION < '1.9'