code: def number_of_trajectories(self, stride=None):
          r
          if not IteratorState.is_uniform_stride(stride):
              n = len(np.unique(stride[:, 0]))
          else:
              n = self.ntraj
          return n
docs: r""" Returns the number of trajectories.
  
          Parameters
          ----------
          stride: None (default) or np.ndarray
  
          Returns
          -------
              int : number of trajectories