code: def intra_mean(self, values):
          
          # TODO Check that quantity is valid
          if values.ndim > 1:
              return np.array([np.mean(values[x,:], axis=0) for x in self.allocations_])
          else:
              return np.array([np.mean(values[x]) for x in self.allocations_])
docs: Calculate the mean of a quantity within strata
  
          Parameters
          ----------
          values : array-like, shape=(n_items,n_class)
              array containing the values of the quantity for each item in the
              pool
  
          Returns
          -------
          numpy.ndarray, shape=(n_strata,n_class)
              array containing the mean value of the quantity within each stratum