code: def standardize(self):
          
  
          if self.preprocessed_data.empty:
              data = self.original_data
          else:
              data = self.preprocessed_data
          
          scaler = preprocessing.StandardScaler()
          data = pd.DataFrame(scaler.fit_transform(data), columns=data.columns, index=data.index)
          self.preprocessed_data = data
docs: Standardize data.