docs: def get_barycenter(self):
          """Return the mass weighted average location.
  
          Args:
              None
  
          Returns:
              :class:`numpy.ndarray`:
          """
          try:
              mass = self['mass'].values
          except KeyError:
              mass = self.add_data('mass')['mass'].values
          pos = self.loc[:, ['x', 'y', 'z']].values
          return (pos * mass[:, None]).sum(axis=0) / self.get_total_mass()