Add uniq_by and uniq_by! to Array.

3 files changed, 41 insertions, 3 deletions

diff --git a/activesupport/lib/active_support/core_ext/array.rb b/activesupport/lib/active_support/core_ext/array.rb
index b583c7533e..4688468a8f 100644
--- a/activesupport/lib/active_support/core_ext/array.rb
+++ b/activesupport/lib/active_support/core_ext/array.rb
@@ -1,5 +1,6 @@
 require 'active_support/core_ext/array/wrap'
 require 'active_support/core_ext/array/access'
+require 'active_support/core_ext/array/uniq_by'
 require 'active_support/core_ext/array/conversions'
 require 'active_support/core_ext/array/extract_options'
 require 'active_support/core_ext/array/grouping'
diff --git a/activesupport/lib/active_support/core_ext/array/uniq_by.rb b/activesupport/lib/active_support/core_ext/array/uniq_by.rb
new file mode 100644
index 0000000000..a09b2302fd
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/array/uniq_by.rb
@@ -0,0 +1,17 @@
+class Array
+  # Return an unique array based on the criteria given as a proc.
+  #
+  #   [1, 2, 3, 4].uniq_by { |i| i.odd? }
+  #   #=> [1, 2]
+  #
+  def uniq_by
+    hash, array = {}, []
+    each { |i| hash[yield(i)] ||= (array << i) }
+    array
+  end
+
+  # Same as uniq_by, but modifies self.
+  def uniq_by!
+    replace(uniq_by{ |i| yield(i) })
+  end
+end
diff --git a/activesupport/test/core_ext/array_ext_test.rb b/activesupport/test/core_ext/array_ext_test.rb
index f5f91ddd80..6f3b28682a 100644
--- a/activesupport/test/core_ext/array_ext_test.rb
+++ b/activesupport/test/core_ext/array_ext_test.rb
@@ -51,9 +51,7 @@ class ArrayExtToParamTests < Test::Unit::TestCase
   end
 end
 
-class ArrayExtToSentenceTests < Test::Unit::TestCase
-  include ActiveSupport::Testing::Deprecation
-  
+class ArrayExtToSentenceTests < ActiveSupport::TestCase  
   def test_plain_array_to_sentence
     assert_equal "", [].to_sentence
     assert_equal "one", ['one'].to_sentence
@@ -320,6 +318,28 @@ class ArrayExtractOptionsTests < Test::Unit::TestCase
   end
 end
 
+class ArrayUniqByTests < Test::Unit::TestCase
+  def test_uniq_by
+    assert_equal [1,2], [1,2,3,4].uniq_by { |i| i.odd? }
+    assert_equal [1,2], [1,2,3,4].uniq_by(&:even?)
+    assert_equal (-5..0).to_a, (-5..5).to_a.uniq_by{ |i| i**2 }
+  end
+
+  def test_uniq_by!
+    a = [1,2,3,4]
+    a.uniq_by! { |i| i.odd? }
+    assert_equal [1,2], a
+
+    a = [1,2,3,4]
+    a.uniq_by! { |i| i.even? }
+    assert_equal [1,2], a
+
+    a = (-5..5).to_a
+    a.uniq_by! { |i| i**2 }
+    assert_equal (-5..0).to_a, a
+  end
+end
+
 class ArrayExtRandomTests < Test::Unit::TestCase
   def test_random_element_from_array
     assert_nil [].rand