<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def ref(self, ref):
 """ Filters the current DataFrame to only contain those rows whose reference is the given reference name. :param ref: Reference to get :type ref: str :rtype: ReferencesDataFrame """

        return ReferencesDataFrame(self.filter(self.name == ref)._jdf,
                                   self._session, self._implicits)