implement transform

  def transform_array(

      self, X: np.ndarray, y: np.ndarray, w: np.ndarray,

      ids: np.ndarray) -> Tuple[np.ndarray, np.ndarray, np.ndarray, np.ndarray]:

    return super().transform_array(X, y, w, ids)

    source = list(map(lambda x: x.split('>')[0] + '>' + x.split('>')[1], X))

    target = list(map(lambda x: x.split('>')[2], X))

    X = np.column_stack((source, target))

    return (X, y, w, ids)

  def untransform(self, transformed):

    return super().untransform(transformed)