This is great - I'm learning some good stuff here. In particular, I'd never thought before about using purrr::map() just to reiterate a function like you did with grow_multi() - (I think - perhaps that was in the previous video). And I've used purrr::reduce() before but never really found a way to get my head round accumulate() - this bit for me, from 9:53, I think is going to be really useful in terms of developing the right functional programming mindset for using accumulate.