Calculate the continental average for each numeric data column: 
header <- c("Life Expectancy", "Population", "GDP per Capita")
temp <- data.frame()
for (continent in unique(gapminder$continent)) {
    current <- c(
        mean(gapminder[gapminder$continent==continent,]$lifeExp, 
             na.rm = TRUE), 
        mean(gapminder[gapminder$continent==continent,]$pop, 
             na.rm = TRUE),
        mean(gapminder[gapminder$continent==continent,]$gdpPercap, 
             na.rm=TRUE))
    temp <- rbind(temp,current)
}
names(temp) <- header
rownames(temp) <- unique(gapminder$continent)
temp
##          Life Expectancy Population GDP per Capita
## Asia            60.06490   77038722       7902.150
## Europe          71.90369   17169765      14469.476
## Africa          48.86533    9916003       2193.755
## Americas        64.65874   24504795       7136.110
## Oceania         74.32621    8874672      18621.609