Split up with keep() and discard()

We want to split our results into two groups: the days over 100, and the days under 100. We'll combine keep() and discard() to do so.

Why two functions? Couldn't we use one function? Couldn't we create a mapper called is_less_than_hundred?

We could, but that would be more error-prone: it's easier to switch from keep() to discard() than copying and pasting. By combining both functions, we only need one mapper. That means that if we want to change the threshold, we'll only need to do it once, not twice, as we would have to do if we had two mappers.

This is a rule you should endeavor to apply when coding: write code so that if you need to change one thing, you will have to change it just once.

all_visits is still available in your workspace.

Map the set_names() function on all_visits to add the name of the days: all_visits_named.
Create a mapper called threshold that will test if .x is over 100.
Create group_over by keeping the elements that are over 100.
Create group_under by discarding the elements that are over 100.

Exercise

Split up with keep() and discard()

Instructions