I have the sense that it may be doable using the "Group" functionality,
but wanted to get clarification first on the User Interactivity.
Do you want the Interactor to select which Markets go into which Group,
or will you be doing that beforehand and just showing them the graphs?
If the latter, you right-click on [Market] and select Create > Group...
This will allow you to arrange the constituents of your 30 market groups
and give the groups names.
Then you can put the [Market (Group)] field onto the Filter shelf.
On your graph, you would just put your market share calculation
as the dual axis and put your [Market] on the color shelf.
Please see workbook v10.3 attached in the Forum Thread.
277092market.twbx 1.2 MB