Why does purrr::pwalk not work when writing CSV-files

Question

I am trying to write simulated testdata to a temporary directory. I will have to write lots of files and I want to write the loops with a function from the purrr package, as these seem to have concise designed syntax. But I cannot get purrr::pwalk to work? What am I doing wrong?

library(data.table)
library(purrr)

# define temporary directory
pp <- withr::local_tempdir()

# define function to write simulated files
f <-
  function(.x,.y) {
    dt <- data.table(country = .x, school_id = 1:2, school_type = c("a","b"))
    fwrite(dt, withr::local_tempfile(pattern = paste0("school.",.x), tmpdir = .y))
  }
# deploy function to write two files
purrr::walk2(.x = c("at","de"), .y = pp, .f = f)

# why no files in pp?
list.files(pp)

I have referenced these:

https://www.tidyverse.org/blog/2023/05/purrr-walk-this-way/

https://adv-r.hadley.nz/functionals.html?q=purrr#purrr-style

Answer 1

withr::local_tempfile gives us a full path, not just a file name. So, the function works as expected, it just writes to another temp folder (created by local_tempfile, not the one that you assigned to pp).

library(data.table)
library(purrr)

pp <- withr::local_tempdir()

fw <- function(.x, .y) {
    dt <- data.table(country = .x, school_id = 1:2, school_type = c("a","b"))
    fwrite(dt, paste(.y, paste0("school.", .x), sep = "/"))
  }

purrr::walk2(.x = c("a","b"), .y = pp, .f = fw)

list.files(pp)
#> [1] "school.a" "school.b"

^{Created on 2024-02-15 with reprex v2.0.2}