#set up some data
mycodat <- read.csv(stdin(),header=TRUE)
country,obsv
Spain,4
Spain,5
Portugal,3
Portugal,7
Venezuala,8
Zambia,2
Zambia,4
Zambia,3

regdat <- data.frame(country=unique(mycodat$country)) # the thing you're trying to get
                                                      # the country means into

# Now generate the summary and put it in the data
regdat$meanobsv <- with(mycodat,tapply(obsv,country,mean))