def cardinal_groupby(self):
g, t = self._cardinal<EOL>self[g] = self[g].astype(t)<EOL>grpby = self.groupby(g)<EOL>self[g] = self[g].astype('<STR_LIT>')<EOL>return grpby<EOL>
Group this object on it cardinal dimension (_cardinal).

Returns:
    grpby: Pandas groupby object (grouped on _cardinal)