Create a named empty list based on dataframe and column names

Question

I want create an empty list which takes on the name of a dataframe and has empty elements inside based on the name of the dataframe

What I've Tried - Does Not Work

my_list_function <- function(thedata) {
  list(
    x = map(names(x), ~ .x = list())
  ))
}

I want to be able to run

my_list_function(mtcars)

and get the output:

Desired Output

list(
  mtcars = list(
    mpg = list(),
    cyl = list(),
    disp = list(),
    hp = list(),
    drat = list(),
    wt = list(),
    qseq = list(),
    vs = list(),
    am = list(),
    gear = list(),
    carb = list()
  )
)

score 3 · Accepted Answer · 2020-04-20 19:21:03Z

3

Using purrr:

library(purrr)
map(mtcars, ~ list())

If you want the name of the data itself in the list, you can try this:

my_list_function <- function(data) {
  .data <- rlang::enquo(data)

  list(map(data, ~ list())) %>% 
    set_names(rlang::as_name(.data))
}

my_list_function(mtcars)

edited Apr 20, 2020 at 19:21

answered Apr 20, 2020 at 19:12

user10917479

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Comments

akrun · Accepted Answer · 2020-04-21 18:47:24Z

1

We can use setNames

my_list_function <- function(data) {
     nm1 <- deparse(substitute(data))
    setNames(list( setNames(rep(list(list()), length(data)), names(data))), nm1)
      }

my_list_function(mtcars)
#$mtcars
#$mtcars$mpg
#list()

#$mtcars$cyl
#list()

#$mtcars$disp
#list()

#$mtcars$hp
#list()
# ...

Or using purrr

library(purrr)
library(dplyr)
my_list_function <- function(data) {


   lst(!! enquo(data) := map(data, ~ list()))
  }
my_list_function(mtcars)
#$mtcars
#$mtcars$mpg
#list()

#$mtcars$cyl
#list()

#$mtcars$disp
#list()

#$mtcars$hp
#list()
# ...

edited Apr 21, 2020 at 18:47

answered Apr 20, 2020 at 19:08

akrun

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3 Comments

user10917479 Over a year ago

Typo with "lst" in the purrr answer. And I don't know if it is an rlang version thing or something but I get Error: :=` can only be used within a quasiquoted argument` as well (I had it in my solution at first and then it stopped working).

akrun Over a year ago

@Adam sorry, lst is found in both tibble and dplyr. I should have updated it

user10917479 Over a year ago

Great. Works now. Good to know, that was effectively what I wanted to do but settled for set_names().

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