    # File lib/standard/facets/random.rb, line 196
        def rand_subset( number=nil, exclusive=true )
          number = Random.number(size) unless number
          number = number.to_int
          #return self.dup if (number >= size and exlusive)
          return sort_by{rand}.slice(0,number) if exclusive
          ri =[]; number.times { |n| ri << Random.number(size) }
          return values_at(*ri)
        end