Exploring world life expectancy

The two data.tables from the previous exercise have been loaded into your workspace:

life_exp: contains the life expectancy of each country in 2010 sourced from the Gapminder foundation
continents: contains a mapping between each country and the continent(s) they are part of built from information provided by Countries-ofthe-World.com.

Your goal this time is to calculate the average life expectancy across countries within each continent.

100 XP

Inner join life_exp to continents and calculate the mean() "years" of life expectancy grouped by the "continent" column.