code: def filter_by_cols(self, cols, ID=None):
          
          rows = to_list(cols)
          fil = lambda x: x in rows
          applyto = {k: self._positions[k][1] for k in self.keys()}
          if ID is None:
              ID = self.ID + '.filtered_by_cols'
          return self.filter(fil, applyto=applyto, ID=ID)
docs: Keep only Measurements in corresponding columns.