Applying a function to groups when missing values

Hi all, I have a huge table made in this way

    ID1 ID2 Date      Occurrences
    1   1   2015-5    9
    1   2   2015-5    11
    1   2   2015-6    1
    1   43  2015-8    2
    2   3   2015-7    40

The primary key of the table is the triple (ID1,ID2,Date).

Now if I want to apply a function to sum how many occurrences a single ID1 has per month, getting rid of ID2, I can use:

    varfun(@sum,data,'InputVariables','Occurrences', GroupingVariables',{'ID1','Date'});

is there a way to expand the grouping such that the dates considered are the all unique values in the Date column? In other words, the month 2015-7 is not present for ID1 = 1, but I would like to get a 0 instead of no row with that value because it is not present after grouping for ID1 = 1

Answer 1

[Savino Dambra]

I kinda solved the problem by making an outer left join with a full table of ID1 and Date. It is not very elegant but it works