Convert list to list of lists

Apply the function list to the list a:

lapply(a, list)

[[1]]
[[1]][[1]]
[1] "A"


[[2]]
[[2]][[1]]
[1] "B"


[[3]]
[[3]][[1]]
[1] "C"

A possible solution, using purrr::map:

library(purrr)

a = list('A', 'B', 'C')
b = list(list('A'), list('B'), list('C'))

a %>% map( ~ list(.x)) %>% identical(b)

#> [1] TRUE

a %>% map( ~ list(.x))

#> [[1]]
#> [[1]][[1]]
#> [1] "A"
#> 
#> 
#> [[2]]
#> [[2]][[1]]
#> [1] "B"
#> 
#> 
#> [[3]]
#> [[3]][[1]]
#> [1] "C"

Or simply:

map(a, list)

Another base R option:

Map(list, a)

Output

[[1]]
[[1]][[1]]
[1] "A"

[[2]]
[[2]][[1]]
[1] "B"

[[3]]
[[3]][[1]]
[1] "C"

Benchmark

As suspected, lapply is the fastest.