R dplyr summarise across remaining columns - r

Question

Using R's dplyr is there a clean way to use the across function to select variables not already captured in other across statements?
For example, I could have a data set that I want to summarise on a 1-to-1 basis (i.e. the output columns have the same structure as the input data set), applying the first function to the character fields, the mean function to a select number of numeric fields and then sum to all remaining fields.
Typically I have a large number of columns with various selection methods, so explicitly working out the remaining columns can be overall onerous. To date, I have found workarounds given the particular data set I am working with but having a generic solution would be very useful.
The code below shows what I would like to run and the resulting output. remaining_columns() is made up.
library(dplyr)
first.if.unique = function(x) if(length(unique(x))==1) x[1] else NA
x = starwars %>% select(species,sex,mass,height) %>% head(10)
cols_to_average = c("mass")
x %>%
group_by(sex) %>%
summarise(
across(where(is.character),first.if.unique),
across(any_of(cols_to_average),mean),
across(remaining_columns(),sum)
)
Input / Output data sets:
> print(x)
# A tibble: 10 x 4
species sex mass height
<chr> <chr> <dbl> <int>
1 Human male 77 172
2 Droid none 75 167
3 Droid none 32 96
4 Human male 136 202
5 Human female 49 150
6 Human male 120 178
7 Human female 75 165
8 Droid none 32 97
9 Human male 84 183
10 Human male 77 182
> print(y)
# A tibble: 3 x 4
sex species mass height
<chr> <chr> <dbl> <int>
1 female Human 62 315
2 male Human 98.8 917
3 none Droid 46.3 360

Answer 1

I personally don't see a way to achieve this apart from specifying the negative previous selections.
x %>%
group_by(sex) %>%
summarise(
across(where(is.character),first.if.unique),
across(any_of(cols_to_average),mean),
across(!where(is.character)&!any_of(cols_to_average),sum)
)
# A tibble: 3 x 4
sex species mass height
<chr> <chr> <dbl> <int>
1 female Human 62 315
2 male Human 98.8 917
3 none Droid 46.3 360