[R-pkg-devel] Writing to files without altering working directory in R package

For what it's worth, the recommendation to use `tempfile()` is very
confusing to R users.

Often users (particularly new users) jump directly to examples when
reading documentation and when you have these more complicated
examples they do not realize they can just use a simple string
literal.

See https://github.com/tidyverse/readr/issues/635 for an issue where
multiple users explicitly request examples which do _not_ use
`tempfile()`.

On Fri, May 3, 2019 at 7:59 PM Duncan Murdoch <murdoch.duncan at gmail.com> wrote:

On 03/05/2019 6:33 p.m., Jarrett Phillips wrote:

Hello,

My R package has a function with an argument to specify whether numerical
results should be outputted to a CSV file.

CRAN policy stipulates verbatim that

Packages should not write in the user?s home filespace (including
clipboards), nor anywhere else on the file system apart from the R
session?s temporary directory (or during installation in the location
pointed to by TMPDIR: and such usage should be cleaned up). Installing into
the system?s R installation (e.g., scripts to its bin directory) is not
allowed.

I know I should use tempdir() within my package function, but I've not seen
any examples on how this is best done within existing R packages.

Within my package documentation examples for my function, I have the lines:

   \dontshow{.oldwd <- setwd(tempdir())}

... some R code ...

\dontshow{setwd(.oldwd)}

but I have been informed that this is not the accepted way.

Any ideas from the community on how do do this properly?

Use the tempfile() function to generate a filename in the temporary
directory.  You might want to use the "pattern" or "fileext" arguments,
but don't change the "tmpdir" argument.

Then write to that file.

For example,

filename <- tempfile(fileext = ".csv")
write.csv(df, filename)

It's a good idea to clean up afterwards using

unlink(filename)