code: def ratio_value_number_to_time_series_length(self, x):
          
          ratio = feature_calculators.ratio_value_number_to_time_series_length(x)
          logging.debug("ratio value number to time series length by tsfresh calculated")
          return ratio
docs: As in tsfresh `ratio_value_number_to_time_series_length <https://github.com/blue-yonder/tsfresh/blob/master\
              /tsfresh/feature_extraction/feature_calculators.py#L830>`_
  
              Returns a factor which is 1 if all values in the time series occur only once,
              and below one if this is not the case.
              In principle, it just returns: # unique values / # values
              
              :param x: the time series to calculate the feature of
              :type x: pandas.Series
              :return: the value of this feature
              :rtype: float