docs: def enrich(self, column1, column2):
          """ This method calculates the difference in seconds between
              the 2 columns (column2 - column1)
  
          The final result may provided negative values depending on the values
          from column1 and column2.
  
          :param column1: first column. Values in column1 must be datetime type
          :param column2: second column. Values in column2 must be datetime type
          :type column1: string
          :type column2: string
  
          :return: original dataframe with a new column with the difference
              between column2 - column1
          :rtype: pandas.DataFrame
          """
  
          if column1 not in self.data.columns or \
             column2 not in self.data.columns:
              return self.data
  
          self.data["timedifference"] = (self.data[column2] - self.data[column1]) / np.timedelta64(1, 's')
          return self.data