Replace values from bottom to top

[Joana Bennet]

Dear Statalists,

I have a dataset in the following shape for several counties and years:

County	Year	Variable
1	1977	-
1	1978	-
1	1979	-
1	1980	3000
1	1981	3000
...	...	...
3	1977	-
3	1978	-
3	1979	-
3	1980	4000
3	1981	4000
...	...	...

For all counties, the values for the years 1977 to 1979 are missing for "Variable" and I want to replace those missings with the value from the year 1980 of the respective county. I could find comments on how to fill in values from the top to the bottom but not vice versa. Does anyone have a suggestion for me? I suppose I will need a loop as I want to replace the values for several counties.
Thank you in advance!

[Nick Cox]

This FAQ

https://www.stata.com/support/faqs/d...issing-values/

is one of various places where this is discussed. In your data example ipolate, epolate would I think also work as you wish.

[Joana Bennet]

Thank you Nick, I could find an answer through the link