def convert_to(ary, type)
      new = []
      ary.each_index do |row|
        new << ary[row].collect {|elem| elem.send(type)}
      end
      new
    end
def convert_to(ary, type)
      new = []
      ary.each_index do |row|
        new << ary[row].collect {|elem| elem.send(type)}
      end
      new
    end
type should be one of :to_s, :to_i, :to_f, :to_r