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

I agree that setwd(), tempdir(), etc. clutter up examples.  At the
same time, I respect the CRAN policy - it's conservative approach has
helped us avoid a wild-west working environment. One approach that
might help bring some standardization, instead of each package
developer rolls their own, and avoid having to have that tempdir code
in there is to have example() handle this.  For example, add a
workdir=tempdir() argument to example() and have example() change to
that directory temporarily, and report on the working directory at the
end.

example(foo)

...
Any output files produced by this example may be found in the
temporary working directory '/tmp/alice/Rtmp4faDCv'.

This could be a message or a warning.  One could also imagine using
workdir=getOption("example.workdir", tempdir()) as the default.  If
properly done, this would allow the user to set
options(example.workdir = quote(getwd())) if they'd like to write to
the current directory.

What it does not solve is when a user cut'n'paste code, but maybe that
could be considered acceptable because in that case the user is not
running/source code, but calling it themself.

My $.02

/Henrik




These messages can be skipped if called with example(...,
workdir=getwd()).

On Tue, May 7, 2019 at 10:57 AM Duncan Murdoch
<murdoch.duncan at gmail.com> wrote:

On 06/05/2019 12:16 p.m., Jim Hester wrote:

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()`.

I think beginners rarely like the help pages, and that's really to be
expected:  help pages need to be complete and correct, and beginners
really need a small subset of possibilities.  Beginners need

tutorials.

In the Github issue, you mentioned pollution of the working

directory,

but I think a bigger problem is destruction of user data, e.g. if a

user

has a file "wine.csv", and the example writes to that file.

So you need to do something to protect users.  I think making

examples a

little complicated by using setwd(tempdir()) with a literal filename,

or

writing to tempfile() is worth it.

Duncan Murdoch

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)