Pandas performance warning

[kyralianaka]

When using GroupView to stimulate, clamp, and insert channels, Pandas raises

PerformanceWarning: DataFrame is highly fragmented. This is usually the result of calling frame.insert many times, which has poor performance. Consider joining all columns at once using pd.concat(axis=1) instead. To get a de-fragmented frame, use newframe = frame.copy()

and references lines

• 252 in base.py (self.nodes.loc[view.index.values, key] = channel.channel_params[key])
• 1646 in base.py (view["controlled_by_param"] = 0)
• 81-83 in network.py (view["global_comp_index"] = view["comp_index"], view["global_branch_index"] = view["branch_index"], view["global_cell_index"] = view["cell_index"])

Other operations may raise this warning as well. I am not sure how much this is reducing performance exactly, but it seems like something that could be addressed.

[jnsbck]

@kyralianaka @huangziwei is this still happening with the new backend? If not you can potentially close this.