Fix up Enumerable#group_by

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@8604 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activesupport/lib/active_support/core_ext/enumerable.rb

@@ -15,15 +15,23 @@ module Enumerable
   #   "2006-02-24 -> Transcript, Transcript"
   #   "2006-02-23 -> Transcript"
   def group_by
-    inject([]) do |groups, element|
-      value = yield(element)
-      if (last_group = groups.last) && last_group.first == value
-        last_group.last << element
+    groups = []
+
+    inject({}) do |grouped, element|
+      index = yield(element)
+
+      if group = grouped[index]
+        group << element
       else
-        groups << [value, [element]]
+        group = [element]
+        groups << [index, group]
+        grouped[index] = group
       end
-      groups
+
+      grouped
     end
+
+    groups
   end if RUBY_VERSION < '1.9'
 
   # Calculates a sum from the elements. Examples:
@@ -64,5 +72,4 @@ def index_by
       accum
     end
   end
-  
 end

activesupport/test/core_ext/enumerable_test.rb

@@ -15,9 +15,13 @@ def test_group_by
       people << p
     end
 
-    objects.group_by {|object| object.name}.each do |name, group|
-      assert group.all? {|person| person.name == name}
+    grouped = objects.group_by { |object| object.name }
+
+    grouped.each do |name, group|
+      assert group.all? { |person| person.name == name }
     end
+
+    assert_equal objects.uniq.map(&:name), grouped.map { |name, group| name }
   end
 
   def test_sums