Combine get_{expressions,observables,states,...}_as_dataframe?

[dweindl]

Currently we have a number of get_*_as_dataframe functions. I think it would be convenient to have a function to get trajectories of all model entities from ReturnData, optionally filtered by a list of model entities.

I am not sure if this should (in the long term) replace, or be an addition to the current functions. Maintenance-wise, a single function would be preferable. Performance-wise, if one really only want to have all observables/state variables/expressions, individual functions may still make sense. I don't think the performance argument is really strong here, so I tend to rather replace the current functions, or temporarily implement them in terms of passing the respective entity IDs to a more general function.

[FFroehlich]

fully agreed!