def bucket_value(index, type = nil)
      case type
      when :begin, :start, :lower, :lower_bound then bucket_lower_bound(index)
      when :end, :finish, :upper, :upper_bound then  bucket_upper_bound(index)
      else bucket_average_value(index)
      end
    end
def bucket_value(index, type = nil)
      case type
      when :begin, :start, :lower, :lower_bound then bucket_lower_bound(index)
      when :end, :finish, :upper, :upper_bound then  bucket_upper_bound(index)
      else bucket_average_value(index)
      end
    end
Returns a single value representing a bucket.