code: def sort_index(self):
          
          sort = sorted_list_indexes(self._index)
          # sort index
          self._index = blist([self._index[x] for x in sort]) if self._blist else [self._index[x] for x in sort]
          # each column
          for c in range(len(self._data)):
              self._data[c] = blist([self._data[c][i] for i in sort]) if self._blist else [self._data[c][i] for i in sort]
docs: Sort the DataFrame by the index. The sort modifies the DataFrame inplace
  
          :return: nothing