Add margin row totals in dplyr chain

Question

I would like to add overall summary rows while also calculating summaries by group using dplyr. I have found various questions asking how to do this, e.g. here, here, and he

Answer 1

If you would like to have truly universal solution you could use a combination of purrr::map_df, base::c and base::sum mtcars %>% purrr::map_df(~c(.x, sum(.x, na.rm=TRUE))) %>% tail

P.S. All columns must be numeric!