(Builds on: Vector functions, purrr basics)

(Leads to: List-columns, purrr map with multiple inputs)

Until now, you’ve been using vector functions inside `mutate()`

to create new
columns. In *Vector functions*, you learned how to convert some scalar functions
into vector functions. Sometimes, however, you’ll want to use a scalar function
to create a new column, and you won’t be able to convert that scalar function
into a vector function.

In this reading, you’ll learn how to create new columns with a scalar function by using a map function to apply that scalar function to each element of an existing column.

- purrr inside mutate [prog-9]