Unquoting argument inside of function in R

Question

I cannot figure out why the bang-bang operator in my function is not unquoting my grp argument. Any help would be much appreciated!

library(dplyr)

test_func <- function(dat, grp){
  dat %>%
    group_by(!!grp) %>%
    summarise(N =  n())
}

test_func(dat = iris, grp = "Species")

Instead of grouping by species it just produces the summary for the entire data:

Answer 1

If we are passing a string, then convert to symbol and evaluate (!!)

test_func <- function(dat, grp){
 dat %>%
    group_by(!! rlang::ensym(grp)) %>%
    summarise(N =  n(), .groups = 'drop')
 }

-testing

test_func(dat = iris, grp = "Species")
# A tibble: 3 x 2
#  Species        N
#* <fct>      <int>
#1 setosa        50
#2 versicolor    50
#3 virginica     50

Or another option is to use across

test_func <- function(dat, grp){
    dat %>%
       group_by(across(all_of(grp))) %>%
       summarise(N =  n(), .groups = 'drop')
 }