Isolating non-unique items in an array

ruby-talk
1

From: Phrogz [mailto:gavin@refinery.com]
class Array
  def duplicates_count
    uniq.map{ |e|
      if ( count = grep(e).size ) > 1
        { e => count }
      end
    }.compact
  end
end

a = ["a", "a", "a", "b", "c", "d", "d"]
p a.duplicates_count
#=> [{"a"=>3}, {"d"=>2}]

Don't listen to that Phrogz character, he's insane!

More like:
class Array
  def duplicates_count
    Hash[ *uniq.map{ |e|
      if ( count = grep(e).size ) > 1
        [e, count]
      end
    }.compact.flatten ]
  end
end

a = ["a", "a", "a", "b", "c", "d", "d"]
p a.duplicates_count
#=> {"a"=>3, "d"=>2}

But of course, other posts in this thread are likely faster.