aggregate data over year and week

[gustavofred]

I want to aggregate data for value a and b over the year-week (or week AND year) and divide.

somehow my approach is not working, what am i doing wrong? im getting "-" as result.

Aggr({1}sum([value a]),year, week )/Aggr({1}sum([value b]),year, week)

my dimensions are year, week, location, year-week currently. Im using a diagram object as a table.

[edwin]

try 

=sum(value_a)/sum(total <year> value_a)