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

[Duncan Murdoch]

On 02/10/2023 10:17 p.m., Trevor Davis wrote:
>  > Thanks!  However, isn't length(dev.list()) == 0 when there are no
> devices?  That's what I'm seeing on MacOS.
> 
> Ifthere 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.

Right, I see.  With some more fiddling, I've decided that I don't like 
the error you get if you try to close device 1, so here's the current 
version:

safe.dev.off  <- function(which = dev.cur(), prev = dev.prev()) {
   if (which != 1) {
     force(prev)
     grDevices::dev.off(which)
   }
   if (length(dev.list()))
     dev.set(prev)
   else
     c("null device" = 1)
}

This does the dev.set even if there's only one device so it can return 
the resulting device number.

Duncan Murdoch

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