curly curly operator doesnt work with map() in R - r

Question

library(tidyverse)
mean_by <- function(data,by,conti){
data %>% group_by({{by}}) %>% summarise(mean=mean({{conti}})) %>%
print() %>%
ggplot(aes(x={{by}},y=mean))+geom_col()
}
map(mtcars %>% select_if(is.numeric),~mean_by(mtcars,cyl,.))
# Not quite the same
mean_by(mtcars,cyl,carb)
I was toying around with the curly curly operator in R (just learned about it!) and then when iterating using map it seemd like the grouping isnt working very well, and I cant get my hands around the problem. What am I doing wrong?
Btw, When trying the explicit pmap way, I couldnt get around using the cyl variable in a clever way
pmap(mtcars %>% select_if(is.numeric),mean_by,..1=mtcars,..2=cyl,..3=.)
Error in pmap():
i In index: 1.
Caused by error in withCallingHandlers():
! object 'cyl' not found
Run rlang::last_error() to see where the error occurred.

Answer 1

It is expecting the column names and not the values - here, the select_if returns a subset of columns that are numeric. We may need the names to loop which would be a string, thus it is better to convert to symbol and evaluate (!!)
library(dplyr)
library(purrr)
mean_by <- function(data,by,conti){
by_sym <- rlang::ensym(by)
conti <- rlang::ensym(conti)
data %>% group_by(!! by_sym) %>%
summarise(mean=mean(!!conti)) %>%
print() %>%
ggplot(aes(x= !!by_sym,y=mean))+geom_col()
}
map(mtcars %>%
select_if(is.numeric) %>%
names,~mean_by(mtcars,cyl, !!.x))
-output (graphs removed)
# A tibble: 3 × 2
cyl mean
<dbl> <dbl>
1 4 26.7
2 6 19.7
3 8 15.1
# A tibble: 3 × 2
cyl mean
<dbl> <dbl>
1 4 4
2 6 6
3 8 8
# A tibble: 3 × 2
cyl mean
<dbl> <dbl>
1 4 105.
2 6 183.
3 8 353.
# A tibble: 3 × 2
cyl mean
<dbl> <dbl>
1 4 82.6
2 6 122.
3 8 209.
# A tibble: 3 × 2
cyl mean
<dbl> <dbl>
1 4 4.07
2 6 3.59
3 8 3.23
# A tibble: 3 × 2
cyl mean
<dbl> <dbl>
1 4 2.29
2 6 3.12
3 8 4.00
# A tibble: 3 × 2
cyl mean
<dbl> <dbl>
1 4 19.1
2 6 18.0
3 8 16.8
# A tibble: 3 × 2
cyl mean
<dbl> <dbl>
1 4 0.909
2 6 0.571
3 8 0
# A tibble: 3 × 2
cyl mean
<dbl> <dbl>
1 4 0.727
2 6 0.429
3 8 0.143
# A tibble: 3 × 2
cyl mean
<dbl> <dbl>
1 4 4.09
2 6 3.86
3 8 3.29
# A tibble: 3 × 2
cyl mean
<dbl> <dbl>
1 4 1.55
2 6 3.43
3 8 3.5

Answer 2

I've not seen the tilde syntax with map, but if you change that it seems to work.
map(mtcars %>% select_if(is.numeric), mean_by, data=mtcars, by=cyl)
Side note, you don't need that print() statement in mean_by.
mean_by <- function(data,by,conti){
data %>% group_by({{by}}) %>% summarise(mean=mean({{conti}})) %>%
ggplot(aes(x={{by}},y=mean))+geom_col()
}