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

maybe that works:

library(dplyr)
mtcars %>%
    # convert cyl column as.character
    mutate_at("cyl",as.character) %>%
    # add a copy of the origina data with cyl column = 'TOTAL'
    bind_rows(mutate(mtcars, cyl="total")) %>%
    group_by(cyl) %>% summarise_all(sum)