code: def side_by_cols(self):
      if not hasattr(self, "_side_by_cols"):
          self._side_by_cols = list(
              set(self.input_que.schema) - set(self._node_repr.outputs)
          )
      return self._side_by_cols
  
label_desc: Use image node_id 2 for calling the SingleInputMixin obj's underlying member method code with example usage: obj.side_by_cols() and returns: self