Pass arugments to R custom function using map (purrr) - r

Question

Using iris for reproducibility
library(tidyverse)
mean_by <- function(data,by,var1) {
data %>%
group_by({{by}}) %>%
summarise(avg=mean({{var1}}))
}
iris %>% mean_by(Species,Petal.Width) # This works
map_dfr(iris,mean_by,Species) # This doesnt work, I want to run this to all numerical columns in iris, how do I do that.
More importantly, fundamental question: how do I pass arguments to custom function using map_dfr in R

Answer 1

Ideally you should use across :
library(dplyr)
library(purrr)
iris %>%
group_by(Species) %>%
summarise(across(where(is.numeric), mean, na.rm = TRUE))
# Species Sepal.Length Sepal.Width Petal.Length Petal.Width
# <fct> <dbl> <dbl> <dbl> <dbl>
#1 setosa 5.01 3.43 1.46 0.246
#2 versicolor 5.94 2.77 4.26 1.33
#3 virginica 6.59 2.97 5.55 2.03
To use map_dfr for numeric variables we can change the function to :
mean_by <- function(data,by,var1) {
data %>%
group_by({{by}}) %>%
summarise(avg = mean(.data[[var1]]))
}
map_dfr(names(select(iris, where(is.numeric))),
mean_by, data = iris, by = Species)
# Species avg
# <fct> <dbl>
# 1 setosa 5.01
# 2 versicolor 5.94
# 3 virginica 6.59
# 4 setosa 3.43
# 5 versicolor 2.77
# 6 virginica 2.97
# 7 setosa 1.46
# 8 versicolor 4.26
# 9 virginica 5.55
#10 setosa 0.246
#11 versicolor 1.33
#12 virginica 2.03