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

[Jim Hester]

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 using 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)
>
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