Create dyadic data

[Thomas Hau]

Dear Stata users

I have a monadic dataset of NATO member countries looking like this:

year country nato
2009 Albania 1
2010 Albania 1
2011 Albania 1
2012 Albania 1
2013 Albania 1
2014 Albania 1
1970 Belgium 1
1971 Belgium 1
1972 Belgium 1
1973 Belgium 1
1974 Belgium 1
1975 Belgium 1

Does anyone know how I can easily create a directed dyadic dataset looking like this

year countrya countryb. nato
2009 Albania Belgium 1
2009 Belgium Albania 1

Any help would be widely appreciated.

Thomas