Return the mass weighted average location.

        Args:
            None

        Returns:
            :class:`numpy.ndarray`:

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()