# File lib/more/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