def _prep_pandas_groupby(self):
        """Prepare the old school pandas group by based approach."""
        myargs = self._myargs
        mykwargs = self._mykwargs

        def extract_keys(groupedFrame):
            for key, group in groupedFrame:
                yield (key, group)

        def group_and_extract(frame):
            return extract_keys(frame.groupby(*myargs, **mykwargs))

        self._baseRDD = self._prdd._rdd()
        self._distributedRDD = self._baseRDD.flatMap(group_and_extract)
        self._mergedRDD = self._sortIfNeeded(
            self._group(self._distributedRDD))
Prepare the old school pandas group by based approach.