Homogenize vectors, lists and values passed as separate arguments to an R function

Question

I am looking for a function that homogenizes vectors composed with c() , lists, and values passed as separate arguments. Consider the following three function calls:

to_list( c(1, 2, 3) )      # Case 1
to_list( list(1, 2, 3) )   # Case 2
to_list( 1, 2, 3 )         # Case 3

The desired output for all three is a list:

# List of 3
#  $ : num 1
#  $ : num 2
#  $ : num 3

purrr::splice() works correctly on Cases 2 and 3. However, for Case 1 it nests the vector inside a list:

# List of 1
#  $ : num [1:3] 1 2 3

I end up needing a "hack" that looks for any such nested vectors, converts them to lists and then unnests the resulting list-of-lists:

library( purrr )
to_list <- function(...) {
  splice(...) %>% map_if( ~(length(.x) > 1), as.list ) %>% flatten()
}

I was wondering if anybody knows a cleaner way of handling all three cases or, better yet, a function that does this already.

Answer 1

Without using any external packages

to_list <- function(...) as.list(unlist(list(...)))
str(to_list(1, 2, 3))
str(to_list(c(1, 2, 3)))
str(to_list(list(1, 2, 3)))

---

Another variation with purrr

to_list <- function(...) list(...) %>%
                            flatten