Exercise

# Expecting mapped output

When you know that the output of your mapped function is an expected type (here it is a numeric vector) you can leverage the `map_*()`

family of functions to explicitly try to return that object type instead of a list.

Here you will again calculate the mean population of each country, but instead, you will use `map_dbl()`

to explicitly append the numeric vector returned by `mean()`

to your dataframe.

Instructions

**100 XP**

- Generate the
`pop_mean`

dataframe using the`map_dbl()`

function to calculate the population mean for each nested dataframe. - Explore the
`pop_mean`

dataframe using`head()`

.