Use input of purrr's map function to create a named list as output in R

Question

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 be

Answer 1

We just need to name the list

names(output) <- input

and then extract the elements based on the name

output$a
#[1] "test-a"

---

If this needs to be done using tidyverse

library(tidyverse)
output <- map(input, ~paste0('test-', .)) %>% 
                                setNames(input)

Answer 2

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Outdated answer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.

Answer 3

The recommended solution:

c("a", "b", "c") %>% 
    purrr::set_names() %>% 
    purrr::map(~paste0('test-', .))