docs: def _add(self, isoel, col1, col2, method, meta):
          """Convenience method for population self._data"""
          self._data[method][col1][col2]["isoelastics"] = isoel
          self._data[method][col1][col2]["meta"] = meta
  
          # Use advanced slicing to flip the data columns
          isoel_flip = [iso[:, [1, 0, 2]] for iso in isoel]
          self._data[method][col2][col1]["isoelastics"] = isoel_flip
          self._data[method][col2][col1]["meta"] = meta