1 files changed, 17 insertions, 0 deletions
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