How to collapse a data by a group and another variable

[walaba]

I have daily measurements which I wanted to collapse by two variables (area and group) by date. As I am not versed in programming skills, I used awkward code of keeping each category of intended variables and then merged the aggregated data as shown below.
My question is how can I collapse this data for each area and group with a short step? I have shared sample data which could be accessed from this link: https://drive.google.com/file/d/0B_S...it?usp=sharing

Thanks
keep if group==1 & area== "urban"
collapse (sum) urban_a_group1 = a urban_b_group1 = b urban_c_group1 = c urban_d_group1 = d, by(date)

[Scott Merryman]

.

egen agg_group = group(date group area), label

collapse (sum) a b c d , by(agg_group)

. l

+---------------------------------------+
| agg_group a b c d |
|---------------------------------------|
1. | 10-Aug-99 1 rural 10 9 19 26 |
2. | 10-Aug-99 1 urban 18 12 18 37 |
3. | 10-Aug-99 2 rural 14 0 3 9 |
4. | 10-Aug-99 2 urban 5 0 6 4 |
5. | 10-Aug-99 3 rural 1 0 0 36 |
|---------------------------------------|
6. | 10-Aug-99 3 urban 22 13 23 49 |
7. | 11-Aug-99 1 rural 12 9 23 26 |
8. | 11-Aug-99 1 urban 8 12 17 37 |
9. | 11-Aug-99 2 rural 10 0 3 9 |
10. | 11-Aug-99 2 urban 5 0 6 4 |
|---------------------------------------|
11. | 11-Aug-99 3 rural 18 0 0 17 |
12. | 11-Aug-99 3 urban 12 29 8 49 |
+---------------------------------------+