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

Here's a take on the accepted answer, using new functions introduced in dplyr 1.0.0 and tidyr 1.0.0.

We pivot the counts using the new tidyr::pivot_wider. Then use the new dplyr::rowwise and dplyr::c_across to sum the counts for the total column.

We can also use tidyr::pivot_longer to get in desired long format.

library(dplyr, warn.conflicts = FALSE)
library(tidyr)

cyl_gear_sum <- mtcars %>%
  count(cyl, gear) %>%
  pivot_wider(names_from = gear, values_from = n, values_fill = list(n = 0)) %>%
  rowwise(cyl) %>%
  mutate(gear_total = sum(c_across()))

cyl_gear_sum
#> # A tibble: 3 x 5
#> # Rowwise:  cyl
#>     cyl   `3`   `4`   `5` gear_total
#>            
#> 1     4     1     8     2         11
#> 2     6     2     4     1          7
#> 3     8    12     0     2         14

# total as row
cyl_gear_sum %>% 
  pivot_longer(-cyl, names_to = "gear", values_to = "n")
#> # A tibble: 12 x 3
#>      cyl gear           n
#>           
#>  1     4 3              1
#>  2     4 4              8
#>  3     4 5              2
#>  4     4 gear_total    11
#>  5     6 3              2
#>  6     6 4              4
#>  7     6 5              1
#>  8     6 gear_total     7
#>  9     8 3             12
#> 10     8 4              0
#> 11     8 5              2
#> 12     8 gear_total    14

^{Created on 2020-04-07 by the reprex package (v0.3.0)}