Calculate a fraction based on multiple conditions

I have data in Stata in this format:

Value	Treatment	Area
1.1	1	1
2.5	1	2
3.4	0	3
6.7	0	1
3.6	0	2
2.9	1	3
2.5	0	1
7.8	1	3

I want to get a sum of the values in "Value" by area and by treatment status. This part I was able to do using:

by Area Treatment, sort: egen desired_variable = total(Value)

What I want is for each row of the dataset, a sum of the values in "Value" for all the treated AND untreated observations in the area. The issue with this is that it gives me the total for Treatment = 1 and Treatment = 0 for each Area, depending on its own treatment status.

I also tried:

by Area, sort: egen desired_variable = total(Value) if treatment == 1

and

by Area, sort: egen desired_variable = total(Value) if treatment == 0

But this is a different version of the same problem, since in a row where the treatment is = 0, the first line of code will just give an NA, and vice versa with the second one.

Solution

This kind of calculation is sometimes needed:

clear
input float value byte(treatment area)
1.1 1 1
2.5 1 2
3.4 0 3
6.7 0 1
3.6 0 2
2.9 1 3
2.5 0 1
7.8 1 3
end

bysort area: egen total1 = total(cond(treatment == 1, value, .)) 
by area: egen total0 = total(cond(treatment == 0, value, .))