Thank you Dariusz, your answer is really useful.
In the meantime I've found even another way to solve my problem, that is: I set the Alternate State of the charts as 'inherited' or 'pre-defined' and then I imposed Group 1 e Group 2 as Alternate States in set analysis in the expressions. In that way I could introduce for each expression a condition for its visualization, condition connected to an event of selection on a field which I created in etl just to contain the names of the expressions. Then if I select 'Sum Sales' in the field, it will appear only 'Sum Sales' in the charts symultaneously.
I admit your solution is more complete and flexible, I will find it useful even in the future.