I am using the map function of the purrr package in R which gives as output a list. Now I would like the output to be a named list based on the input. An example is given below.
input <- c("a", "b", "c")
output <- purrr::map(input, function(x) {paste0("test-", x)})
From this I would like to access elements of the list using:
output$a
Or
output$b
Update
Now in 2020 the answer form @mihagazvoda describes the correct approach: simply set_names before applying map
c("a", "b", "c") %>%
purrr::set_names() %>%
purrr::map(~paste0('test-', .))
Outdated answer
The accepted solution works, but suffers from a repeated argument (input) which may cause errors and interrupts the flow when using piping with %>%.
An alternative solution would be to use a bit more power of the %>% operator
1:5 %>% { set_names(map(., ~ .x + 3), .) } %>% print # ... or something else
This takes the argument from the pipe but still lacks some beauty. An alternative could be a small helper method such as
map_named = function(x, ...) map(x, ...) %>% set_names(x)
1:5 %>% map_named(~ .x + 1)
This already looks more pretty and elegant. And would be my preferred solution.
Finally, we could even overwrite purrr::map in case the argument is a character or integer vector and produce a named list in such a case.
map = function(x, ...){
if (is.integer(x) | is.character(x)) {
purrr::map(x, ...) %>% set_names(x)
}else {
purrr::map(x, ...)
}
}
1 : 5 %>% map(~ .x + 1)
However, the optimal solution would be if purrr would implement such behaviour out of the box.
c("a", "b", "c") %>%
purrr::set_names() %>%
purrr::map(~paste0('test-', .))