Now I get the scenario. The answer you've just found is one of the possible. You can solve it with AGGR() too.
I've loaded the following test data:
LOAD * INLINE [
Mary , 05/01/2015
Below there are three expressions/columns:
1. The first one is your problem scenario, if I got it right.
2. The second one is your solution, counting couples of "name-date".
3. The third is a solution using AGGR(). Note the Sum used over the AGGR count.
My answer came a little late, but I still wanted to mention the AGGR alternative.