On 26/04/2018 1:04 PM, Henrik Bengtsson wrote:
On Thu, Apr 26, 2018 at 6:28 AM, Spencer Graves
<spencer.gra...@effectivedefense.org> wrote:
On 2018-04-26 07:11, Jose A Guijarro wrote:
El 25/04/18 a las 20:21, Duncan Murdoch escribió:
On 25/04/2018 1:32 PM, Sarah Goslee wrote:
Don't change the working directory! That has all kinds of unpleasant
side effects for the unsuspecting user, possibly even more so than
writing to a file.
Instead, write the file to the temp directory, and read it from there,
with e.g.
wd <- tempdir()
write(dat, file.path(wd, 'Ttest_1981-2000.dat'))
Using file.path() means that the appropriate path delimiter for that
OS will be used.
That's one good way to do it. But it is possible to change directory and
change back at the end of the example. For example,
wd <- tempdir()
savedir <- setwd(wd)
... # the original code that writes and reads in the current dir
setwd(savedir)
There's a worry that an error in the middle of the code will leave the
user in the wrong place. If that's really unlikely to happen, then this
code is a little simpler than Sarah's suggestion.
If it is likely, you can use tryCatch(..., finally = setwd(savedir)), but
I think Sarah's solution would be preferable in most cases: many users will
not understand what tryCatch() does.
Hi, Duncan, et al.:
Under what circumstances should one also use "on.exit":
wd <- tempdir()
savedir <- setwd(wd)
on.exit(setwd(savedir))?
Even senior R programmers may miss a failure mode. In a function,
this works well: I don't need to remember to "setwd(savedir)" later in the
code, which could be a problem if I have multiple exit points. I don't know
how it would work in a vignette or the examples section of a *.Rd file.
tryCatch(..., finally = setwd(savedir)) condenses this into one line ... and
is too terse for me in many cases.
FWIW, it can also be used in a local() call, e.g.
local({
wd <- tempdir()
savedir <- setwd(wd)
on.exit(setwd(savedir))
[...]
})
Thanks for pointing that out. That also has the advantage that it
doesn't wipe out variables named "wd" and "savedir".
On the other hand, it has the disadvantage that it doesn't leave wd and
savedir behind for the user to examine, and cut and paste of the central
executable lines won't work, you need to cut the whole local() call.
Duncan Murdoch
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