Copying Observations from Row

[Umar Kathjoo]

My data looks somewhat like this:

Exporter	Importer	Pairid	Year	Trade Value (USD)	Distance	CLanguage	Contiguity	RTA
United States	Canada	1	2018	25614.23	25468	1	1	1
United States	Canada	1	2019	546589.45	25468	1	1	1
United States	Canada	1	2020	546589.54
United States	Canada	1	2021	654585.28
India	China	2	2019	213131.58	24569	0	1	1
India	China	2	2020	121565.25
India	China	2	2021	565454.65

(I just need to copy the missing values in rows for years 2020 and 2021 from year 2019 individually for each country pair with different Pairid)

I have missing values for a few variables like (Distance, Contiguity, RTA) for all country pairs like United States and Canada with Pairid 1 for year 2020 and 2021. Keeping the new value of trade for years 2020 and 2021, I just want to copy the values of other variables from year 2019 to 2020 and 2021. I have a large number of Country Pairs like this with new trade data but no data on other variables. I just want to copy the observations for each country pair in 2019 and paste it for years 2020 and 2021 without copying or pasting the pairid or trade value.

[William Lisowski]

Something like

bysort Pairid (Year):  replace Distance = Distance[_n-1] if missing(Distance)

for each of the variables that you need to carry forward.