code: def _get_binner(self):
          
  
          binner, bins, binlabels = self._get_binner_for_time()
          bin_grouper = BinGrouper(bins, binlabels, indexer=self.groupby.indexer)
          return binner, bin_grouper
docs: Create the BinGrouper, assume that self.set_grouper(obj)
          has already been called.