Hi I have a data on number of countries

and I want to run the regression on combination of countries please how I can do that Please.

country1 country2 country3 country4 country5


reghdfe y x1 x21, a(yearofbirth)




I want to run regression for


country1 country2 country3 country4

country1 country2 country3 country5

and so on for possible combinations


Thanks