variable xxx already defined error r110

[LIU Chenguang]

Hey guys!

I'm using stata do—file to do a multi—period PSM appending on a panel dataset(which will then be used for did regression), the code is as follows:

forvalues i = 2007/2021{
use "C:\Users\lcg19\Desktop\论文\新数据分析2（空气质量标准对违约风险的 影响）\ dataset 6.24.dta",clear
keep if Year==`i'
set seed 20220626
gen tmp=runiform()
sort tmp
psmatch2 Treated $ctrlvars , out(DDBhsh) logit neighbor(2) common ate
drop if _weight==.
save psmdid_`i',replace
}
use psmdid_2007,clear
forvalues i = 2008/2021{
append using psmdid_`i'
}

and after running stata gives me:
do "C:\Users\lcg19\Desktop\论文\新数据分析2（空气质量标准对违约风险的影响）\ 稳健性检验\PSMDID逐期匹配.do"

.
. forvalues i = 2007/2021{
2. use "C:\Users\lcg19\Desktop\论文\新数据分析2（空气质量标准对违约风险的影响）\ dataset 6.24.dta",clear
3. keep if Year==`i'
4. set seed 20220626
5. gen tmp=runiform()
6. sort tmp
7. psmatch2 Treated $ctrlvars , out(DDBhsh) logit neighbor(2) common ate
8. drop if _weight==.
9. save psmdid_`i',replace
10. }
(0 observations deleted)
variable tmp already defined
r(110);

I'm wondering what's wrong with my program, can anybody help me out? Thanks a lot!

[Mike Lacy]

After the first pass through your loop, the variable tmp exists, and -gen- won't allow you to -gen- an existing variable. You can do one of two things, use -replace-, or drop tmp each time after you use it.

gen tmp = .
forvalues .... {
...
   replace tmp = runiform()
...
}

or

forvalues ....  {
   gen tmp = runiform()
...
..
   drop tmp
}