Then I want to calculate the value spent per person per year (having a certain year selected, I want to know how much each person spent for example in 2013). -> I have to aggregate person ID and year.
I'm using this formula:
, [Person ID])), Year))
but it only returns the person who spent most each year, as shown in the picture.
And afterwards I would like to calculate the value spent per person per month (having a certain year and month selected, I want to know how much each person spent for example in January 2015). -> I have to aggregate person ID, year and Month.
Within a table which contained the detail-dimensions you didn't need an aggr-function - they are only useful if you have a consolidated view and wanted to know the aggregation of a calculation on lower dimensions and then you would need sum(aggr(sum for this and not max(aggr(sum.
In your table you need more something like this: sum(TOTAL <Year> Value).