Mimicking a secondary tidy dots argument in an R function - r

Question

I'm looking to create a function that accepts a list of (data frame) variables as one of its parameters. I've managed to get it working partially, but when I get to the group_by/count, things fall apart. How can I do this??
## Works
f1 <- function(dfr, ..., split = NULL) {
dots <- rlang::enquos(...)
split <- rlang::enquos(split)
dfr %>%
select(!!!dots, !!!split) %>%
gather('type', 'score', -c(!!!split))
}
## does not work
f2 <- function(dfr, ..., split = NULL) {
dots <- rlang::enquos(...)
split <- rlang::enquos(split)
dfr %>%
select(!!!dots, !!!split) %>%
gather('type', 'score', -c(!!!split))
count(!!!split, type, score)
}
I would want to do things like
mtcars %>% f2(drat:qsec)
mtcars %>% f2(drat:qsec, split = gear)
mtcars %>% f2(drat:qsec, split = c(gear, carb)) ## ??
These calls with f1() all work, but for f2 none of the commands work. They all end up with a Error in !split : invalid argument type. That f2(drat:qsec) doesn't (immediately) work without the split argument, I'm not too surprised about, but how to get the second and third comment working?

Answer 1

The issue with the second function (the missing pipe notwithstanding) is that count() (or rather group_by() which is called by count()) doesn't support tidyselect syntax so you can't pass it a list to be spliced like you can with select(), gather() etc. Instead, one option is to use group_by_at() and add_tally(). Here's a slightly modified version of the function:
library(dplyr)
f2 <- function(dfr, ..., split = NULL) {
dfr %>%
select(..., {{split}}) %>%
gather('type', 'score', -{{split}}) %>%
group_by_at(vars({{split}}, type, score)) %>% # could use `group_by_all()`
add_tally()
}
mtcars %>% f2(drat:qsec)
# A tibble: 96 x 3
# Groups: type, score [81]
type score n
<chr> <dbl> <int>
1 drat 3.9 2
2 drat 3.9 2
3 drat 3.85 1
4 drat 3.08 2
5 drat 3.15 2
6 drat 2.76 2
7 drat 3.21 1
8 drat 3.69 1
9 drat 3.92 3
10 drat 3.92 3
# ... with 86 more rows
mtcars %>% f2(drat:qsec, split = c(gear, carb))
# A tibble: 96 x 5
# Groups: gear, carb, type, score [89]
gear carb type score n
<dbl> <dbl> <chr> <dbl> <int>
1 4 4 drat 3.9 2
2 4 4 drat 3.9 2
3 4 1 drat 3.85 1
4 3 1 drat 3.08 1
5 3 2 drat 3.15 2
6 3 1 drat 2.76 1
7 3 4 drat 3.21 1
8 4 2 drat 3.69 1
9 4 2 drat 3.92 1
10 4 4 drat 3.92 2
# ... with 86 more rows