[Rd] Problems caused by dev.off() behaviour

[Trevor Davis]

> Thanks!  However, isn't length(dev.list()) == 0 when there are no
devices?  That's what I'm seeing on MacOS.

If there is only one graphics device then R should automatically set it as
the active graphics device so it isn't really necessary to manually set
it.  Although there wouldn't be any harm in manually setting it you only
really need to worry about setting the previous graphics device when there
are two or more devices open.

Trevor

On Mon, Oct 2, 2023 at 5:25 PM Duncan Murdoch <murdoch.duncan using gmail.com>
wrote:

> Thanks!  However, isn't length(dev.list()) == 0 when there are no
> devices?  That's what I'm seeing on MacOS.
>
> Duncan Murdoch
>
> On 02/10/2023 4:21 p.m., Trevor Davis wrote:
> >  > Use it just like dev.off(), but it *will* restore the previous device.
> >
> > I'm observing that if there were no previously open graphics devices
> > then your `safe.dev.off()` opens up a new graphics device which may be
> > an undesired side effect (because "surprisingly" `dev.set()` on the null
> > graphics device opens up a new graphics device).  To avoid that you
> > could check if `dev.list()` is greater than length 1L:
> >
> >     safe.dev.off  <- function(which = dev.cur(), prev = dev.prev()) {
> >       force(prev)
> >       dev.off(which)
> >       if (length(dev.list()) > 1L) {
> >         dev.set(prev)
> >       }
> >     }
> >
> > Trevor
> >
> > On Mon, Oct 2, 2023 at 11:54 AM Duncan Murdoch <murdoch.duncan using gmail.com
> > <mailto:murdoch.duncan using gmail.com>> wrote:
> >
> >     I found some weird behaviour and reported it as
> >     https://bugs.r-project.org/show_bug.cgi?id=18604
> >     <https://bugs.r-project.org/show_bug.cgi?id=18604> and
> >     https://github.com/yihui/knitr/issues/2297
> >     <https://github.com/yihui/knitr/issues/2297>, but it turns out it
> >     was user
> >     error.
> >
> >     The dev.off() function was behaving as documented, but it behaves in
> an
> >     unexpected (by me) way, and that caused the "bugs".
> >
> >     The issue is that
> >
> >          dev.off()
> >
> >     doesn't always result in the previous graphics device being made
> >     current.  If there are two or more other open graphics devices, it
> >     won't
> >     choose the previous one, it will choose the next one.
> >
> >     I'm letting people know because this might affect other people too.
> If
> >     you use dev.off(), don't assume it restores the previous device!
> >
> >     Here's my little workaround alternative:
> >
> >         safe.dev.off  <- function(which = dev.cur(), prev = dev.prev()) {
> >           force(prev)
> >           dev.off(which)
> >           dev.set(prev)
> >         }
> >
> >     Use it just like dev.off(), but it *will* restore the previous
> device.
> >
> >     Duncan Murdoch
> >
> >     ______________________________________________
> >     R-devel using r-project.org <mailto:R-devel using r-project.org> mailing list
> >     https://stat.ethz.ch/mailman/listinfo/r-devel
> >     <https://stat.ethz.ch/mailman/listinfo/r-devel>
> >
>
>

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