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

Duncan Murdoch murdoch@dunc@n @end|ng |rom gm@||@com
Wed May 8 14:08:40 CEST 2019

On 08/05/2019 7:16 a.m., Boris Steipe wrote:
> Have you considered putting the explicit case into a comment? Something like ...
> # For output to a CSV file, we would assign: myCSV <- "myResults.csv"
> # ... but for this example we will use the value of tempfile() as the file name:
> myCSV <- tempfile()
> results <- doSomething(x, csvFile = myCSV, ...)

That seems like a good idea.  If the lack of string literals in the 
example was the issue, you might show the whole command in a comment 
with a string literal:

# This would create "myResults.csv" in the current working directory:
#   results <- doSomething(x, csvFile = "myResults.csv", ...)

# We will create a temporary file instead, with its name in myCSV...

myCSV <- tempfile()
results <- doSomething(x, csvFile = myCSV, ...)

> I often find the lack of comments in examples less than optimal for didactic reasons.
> $0.02
> Boris
>> On 2019-05-07, at 18:50, Duncan Murdoch <murdoch.duncan using gmail.com> wrote:
>> On 07/05/2019 6:44 p.m., Uwe Ligges wrote:
>>> On 07.05.2019 19:57, Duncan Murdoch 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.
>>> Thank you, Duncan. Well, setwd(tempdir()) should be made local to the
>>> examples if used at all, as the user may not expect to have the working
>>> directory changed.
>> Yes, I agree.
>> Duncan Murdoch
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