Compute vaccine effectiveness by groups?

[Bisaloo]

Something that was discussed during the vacineff challenge is whether we want vaccineff functions to be able to deal with grouped data out of the box.
One example would be to compute vaccine effectiveness by country in a dataset including multiple countries.

Pros of computing by groups:

• code could be slightly more efficient than requiring the user to create a loop since we can use vectorized operations
• fewer lines of code for users

Cons of computing by groups:

• necessity to add a new argument, which makes the package slightly more difficult to learn
• slightly more lines of code in package

No matter what is chosen, there should be an example showing how effectiveness can be computed for multiple groups.

[chartgerink]

Is this question still relevant or has it been parked since? (given that this issue is rather stale by now)