Dear All,
I have data on trade agreements and membership to the WTO between country (i) and country (j). My data looks something like:

Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input str3(country_i country_j) int year byte(gatt pta)
"AUS" "BRA" 1986 0 0
"AUS" "BRA" 1987 0 0
"AUS" "BRA" 1988 0 1
"AUS" "BRA" 1989 0 1
"AUS" "BRA" 1990 0 1
"AUS" "BRA" 1991 0 1
"AUS" "BRA" 1992 1 1
"AUS" "BRA" 1993 1 1
"AUS" "BRA" 1994 1 1
"BRA" "AUS" 1986 0 0
"BRA" "AUS" 1987 0 0
"BRA" "AUS" 1988 1 0
"BRA" "AUS" 1989 1 0
"BRA" "AUS" 1990 1 1
"BRA" "AUS" 1991 1 1
"BRA" "AUS" 1992 1 1
"BRA" "AUS" 1993 1 1
"BRA" "AUS" 1994 1 1
end

The gatt membership year between AUS-BRA pair is 1992 whereas between BRA-AUS pair , it is year 1988. I want to pick the minimum year (earliest year between the symmetric pairs). How can i do that in STATA ?
similarly the pta between between AUS-BRA pair is 1988 whereas between BRA-AUS pair, the agreement year is1990. Similarily, i want to pick the minimum year of agreement signing between the country pairs which are symmetric .

Thank you