Not 100% sure I understand exactly what you want but here are some examples of what you can do.
Set analysis:
=sum({$<[Month]={'January'}>}[Sales])
=sum({$<[Month]={'February'}>}[Sales])
etc.
aggr Function:
Let's say you want to sum the invoices for customers that have been with the company less than 180 days (let's also assume you don't have a [Length with Company] field or anything like that) but you only want to show the dimension [City]. You could use the following expression:
=sum
)
aggr
(
if(today()-[Join Date]<180,
sum([Invoice Total])
)
,[Account Number]
)
)
In the above example you can't use set analysis because the [Join Date] of every customer is going to be different and the set analysis is calculated once per chart, not once per row. Also use the dimension [City] for the example above. You're quesiton was pretty vague but hopefully that helped a little bit.
