code: def _get_norms_of_rows(data_frame, method):
      
      if method == 'vector':
          norm_vector = np.linalg.norm(data_frame.values, axis=1)
      elif method == 'last':
          norm_vector = data_frame.iloc[:, -1].values
      elif method == 'mean':
          norm_vector = np.mean(data_frame.values, axis=1)
      elif method == 'first':
          norm_vector = data_frame.iloc[:, 0].values
      else:
          raise ValueError("no normalization method '{0}'".format(method))
      return norm_vector
docs: return a column vector containing the norm of each row