st: Looping over observations that do not start from 1

[George Chioran <george_chioran@yahoo.com>]

Dear Statalisters,

I have a data set that spans from april 2008 to june 2009. I want to loop over the the months in this data set by year. However if I group the months, in year 2008 I have a month variable that starts from 4 and lasts to 12.

While looping over years, I wanted to know if there is a way to loop over the month variable even if it starts from 4.

I was thinking that this could be done if there were a command to skip a repetition from a loop if there are no observations in the database (as with each loop I am keeping the observations that are equal to the current number, thus in year 2008, there are no months 1,2 and 3, so keep if month = `i' would yield an empty table). In my case, the loop would have to skip the first 3 repetitions and start from 4 to run my program. 

My program is similar to this:

egen year = group(year)
su year
local years = _result(6)
local i = 1
while `i' <= `years' {
save file1, replace
keep if year == `i'
su month
local months = _result(6)
local j = 1
while `j' <= `months' {
save file2, replace
keep if month = `j'
local `j' = result from equation
use file2, clear
local j = `j' +1
}
use file1, clear
local i = `i'+1
}


Thank you a lot for the help, 
George


      
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