docs: def transform(self, y):
          """
          Transform features per specified math function.
          :param y:
          :return:
          """
          if self.transform_type == 'log':
              return np.log(y)
          elif self.transform_type == 'exp':
              return np.exp(y)
          elif self.transform_type == 'sqrt':
              return np.sqrt(y)
          elif self.transform_type == 'sin':
              return np.sin(y)
          elif self.transform_type == 'cos':
              return np.cos(y)
          elif self.transform_type == 'tan':
              return np.tan(y)
          elif self.transform_type == 'abs':
               return np.abs(y)