Dear All,

I'm new on Statalist and I'm still figuring out how to use dataex so apologies for my dataset example below. reporter_iso and partner_iso are string variables. Meanwhile, id is generated by egen=group(reporter_iso partner_iso). I need to generate the variable "sum" which cumulatively adds up the changes in "TA_envi_tot" across reporter-partner pairs and years.

I tried these codes but I don't get to generate the values in the "sum" column below:

bysort id (year): gen sum=TA_envi_tot[_n] + TA_envi_tot[_n+1] if TA_envi_sum[_n]!=TA_envi_tot[_n-1]
bysort id (year): replace sum = sum[_n-1] if missing(sum)

id reporter_iso partner_iso year TA_envi_tot sum
3271 ATG DEU 1981 0 0
3271 ATG DEU 1982 0 0
3271 ATG DEU 1983 0 0
3271 ATG DEU 1984 36 36
3271 ATG DEU 1985 36 36
3271 ATG DEU 1986 36 36
3271 ATG DEU 1987 67 103
3271 ATG DEU 1988 67 103
3271 ATG DEU 1989 67 103
4217 BDI BEL 1981 3 3
4217 BDI BEL 1982 3 3
4217 BDI BEL 1983 3 3
4217 BDI BEL 1984 35 38
4217 BDI BEL 1985 35 38
4217 BDI BEL 1986 35 38
4217 BDI BEL 1987 35 38
4217 BDI BEL 1988 36 74
4217 BDI BEL 1989 36 74
4217 BDI BEL 1990 36 74
Thanks a lot for your help!