Please use R write:

What is the county with the *current* (e.g., on the most recent date) highest number of cases in each state?

Use the `group_by()` function

Your answer should be a *vector* of "location" (`county_state`) names, stored in the variable `highest_case_locations_by_state`

Data frame: county_df

Data frame columns: date, county_state, county, state, fips, cases, deaths