You can use the sort by expression option in the chart and use a variable as expression like this:
Control the contents of the variable by using an action in the objects from which you would like to control the sort order.
E.g. set the contents of vExpression to Sum(Sales) for ascending or 1/Sum(Sales) for descending order (depending on what order you have set on the expression in the chart offcourse). The contents of the variable should be text (so leave out the = sign)
You can use interactive sorting by button & variable. Ihad used this feature in many places... it gives the users the flexibility tosort the data. Please look at the attached example and let me know if you needany help!
Hope this helps!
Cheers - DV