在Stata中使用循环生成变量总和

Question

I'm having some problems with a loop that I'm trying to perform and probably with the syntax for generating the variable that I want.

Putting in words, what I am trying to do make is a sum of a particular set of observations and storing each sum in a cell for a new variable. Here is an example of syntax that I used:

forvalues j=1/50 { replace x1 = sum(houses) if village== j' & year==2010 }

gen x2=. forvalues j=1/50 { replace x2 = sum(houses) if village== gen x2=. forvalues j=1/50 { replace x2 = sum(houses) if village== j' & year==2011 }

gen x3 =. forvalues j=1/50 { replace x3 = sum(houses) if village== gen x3 =. forvalues j=1/50 { replace x3 = sum(houses) if village== j' & year==2012 }

This is from a dataset with more than 4000 observations. So, for each particular j, if I were successful with the code above, I would get an unique observation for each j (what I want to obtain), but I'm not obtaining this -- which is a sum of all houses, conditioned with the year and village; the total sum of houses per village in each year. I would greatly appreciate if someone could help me obtain one particular observation for each j in each variable.

Answer 1

sum() will return a running sum, so that is probably not what you want. This type of problem is usually much easier to solve with the by: prefix in combination with the egen command. The one line command below will give you the total number of houses per village and year:

bys village year: egen Nhouses = total(houses)