def factors
      index = @data.sorted_indices
      index.reduce([]){|memo, val| memo.push(@data[val]) if memo.last != @data[val]; memo}
    end
def factors
      index = @data.sorted_indices
      index.reduce([]){|memo, val| memo.push(@data[val]) if memo.last != @data[val]; memo}
    end
uniq