# File lib/facets/core/array/rand_subset.rb, line 22
  def rand_subset( number=nil, exclusive=true )
    number = rand( 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 << rand( size ) }
    return values_at(*ri)
  end