If you have two dimensions, Category and Brand, and your sales field is called Sales, I think it's just
=sum( Sales) / sum(total<Category> Sales)
as expression, i.e. you just need an appropriate total qualifier with dimension list. Please check also the Help.
Then you could format the share e.g in number tab as percentage.
Yes , also , i have a y-axis value as well or a column dimension , which is Branch , and the formula above would only give me the share of the sales of one dimension over the total of the other , but it would not give me the share depending on the y-axis dimension . i should've clarified it better .
Maybe an example would help me to understand - it's still a bit unclear to me, but I still think the total qualifier should be the one here,
=sum(Sales) / sum(total<Category, Branch> Sales)
=sum(Sales) / sum(total<Branch> Sales)
just include in the total qualifier field list all dimensions that you need to group by.