code: def transform(self, y):
          
          if isinstance(y, pd.DataFrame):
              x = y.ix[:,0]
              y = y.ix[:,1]
          else:
              x = y[:,0]
              y = y[:,1]
          if self.transform_type == 'add':
              return pd.DataFrame(np.add(x, y))
          elif self.transform_type == 'sub':
              return pd.DataFrame(np.subtract(x, y))
          elif self.transform_type == 'mul':
              return pd.DataFrame(np.multiply(x, y))
          elif self.transform_type == 'div':
              return pd.DataFrame(np.divide(x, y))
          elif self.transform_type == 'rem':
              return pd.DataFrame(np.remainder(x, y))
          elif self.transform_type == 'pow':
              return pd.DataFrame(x**y)
docs: Transform features per specified math function.
          :param y:
          :return: