R Language Your-Turn Solutions

YOUR TURN #1

countries2 <- countries[countries$EU == 'no' & countries$coastline == 'no',
                        c('country','population')]
countries2[order(countries2$country, decreasing=TRUE),]
# Alternate last line: countries2[order(-as.numeric(countries2$country)),]

YOUR TURN #2

south <- cities[cities$latitude < 40,]
north <- cities[cities$latitude > 60,]
print(aggregate(south$temperature, by=list(south$country), FUN=mean))
print(aggregate(north$temperature, by=list(north$country), FUN=mean))