R Need to restart RStudio to view and save in a file using dev.copy() and dev.off()

Question

I am trying to create a plot and eventually save it as a file. But because I am making a lot of changes and want to test it out, I want to be able to view and save the plot at the same time. I have looked at this page to do what I want to do but in my system, it does not seem to be working as it is supposed to.

Here are my codes:

png('Save.png')

sample.df <- data.frame(group =  c('A','B','A','C','B','A','A','C','B','C','C','C','B'),
X = c(2,11,3,4,1,6,3,7,5,9,10,2,8),
Y = c(3,8,5,2,7,9,3,6,6,1,3,4,10))

plot(Y ~ X, data = sample.df)

dev.copy(png, 'Save.png')
dev.off()

There are several issues (I am new to R so I might be missing something entirely):

(1) When I use png(), I cannot view the plot in RStudio so I used dev.copy() but it does not allow me to view my plot in R studio

(2) Even after I use dev.off(), I cannot view the saved file until I close the RStudio (says "Windows Photo Viewer can't open this picture because the picture is being edited in another program"). I need to restart every time so it is very inconvenient.

What am I doing wrong and how could I view and view saved file without restarting RStudio every time? Thank you in advance!

Addition

Based on Love Tätting's comments, when I run dev.list(), this is what I get.

> png('Save.png')
> 
> sample.df <- data.frame(group =  c('A','B','A','C','B','A','A','C','B','C','C','C','B'),
+                         X = c(2,11,3,4,1,6,3,7,5,9,10,2,8),
+                         Y = c(3,8,5,2,7,9,3,6,6,1,3,4,10))
> 
> plot(Y ~ X, data = sample.df)
> 
> dev.copy(png, 'Save.png')
png 
  3 
> dev.off()
png 
  2 
> dev.list()
png 
  2 
> dev.off()
null device 
          1 
> dev.list()
NULL

Why do I not get RStudioGD?

Answer 1

RStudio has its own device, "RStudioGD". You can see it with dev.list(), where it by default is the first and only one.

R's design for decoupling rendering and backend is by the abstraction of devices. Which ones you can use is platform and environment dependent. dev.list() shows the stack of current devices.

If I understand your problem correctly you want to display the graph first in RStudio, and then decide whether you want to save it or not. Depending on how often you save th image you could use the 'export' button in the plot pane in RStudio and save it manually.

Otherwise, your choice of trying to copy it would be the obvious one for me as well.

To my knowledge the device abstraction in R does not allow one to encapsulate the device as an object, so one for example could make it an argument to a function that does the actual plot. Since dev.set() takes an index as argument, passing the index as argument will be dependent on state of the stack of devices.

I have not come up with a clean solution to this myself and have sometimes retorted to bracketing the plot rendering code with a call to a certain device and saving it right after, and switching device depending on a global.

So, if you can, use RStudios export functionality, otherwise an abstraction would need to maintain the state of the global stack of devices and do extensive testing of its state as it is global and you cannot direct a plot call to a certain device, it simply plots to the current device (to my knowledge).

---

Edit after OP comment

It seems that it is somewhat different behaviour you are experiencing if you cannot watch the file after dev.off, but also need to quit RStudio. For some type of plot frameworks there is a need to call print on the graphical object to have it actually print to the file. Perhaps this is done by RStudio at shutdown as part of normal teardown procedures of open devices? In that ase the file should be empty if you forcibly look in its contents before quiting RStudio. The other thing that sometimes work is to call dev.off twice. I don't know exactly why, but sometimes more devices get created than I have anticipated. After you have done dev.off, what does dev.list show?

---

Edit after OP's edit

I can see that you do, png(); dev.copy(); dev.off(). This will leave you with one more device opened than closed. You will still have the first graphics device that you started open as can be seen when you do the listing. You can simply remove dev.copy(). The image will be saved on dev.off() and should be able to open from the filesystem.

As to why you cannot see the RStudio graphics device, I am not entirely sure. It might be that other code is messing with your device stack. I would check in a clean session if it is there to make sure other code isn't tampering with the device stack. From RStudio forums and other SO questions there seem to have been plot pane related problems in RStudio that have resolved after updating RStudio to the latest. If that is a viable solution for you I would try that.

Answer 2

I've just added support for RStudio's RStudioGD device to the developer's version of R.devices package (I'm the author). This will allow you to do the following in RStudio:

library("R.devices")

sample.df <- data.frame(
  group =  c('A','B','A','C','B','A','A','C','B','C','C','C','B'),
  X = c(2,11,3,4,1,6,3,7,5,9,10,2,8),
  Y = c(3,8,5,2,7,9,3,6,6,1,3,4,10)
)

figs <- devEval(c("RStudioGD", "png"), name = "foo", { 
  plot(Y ~ X, data = sample.df)
})

You can specify any set of output target types, e.g. c("RStudioGD", "png", "pdf", "x11"). The devices that output to file will by default write the files in folder figures/ with filenames as <name>.<ext>, e.g. figures/foo.png in the above example.

The value of the call, figs, holds references to all figures produced, e.g. figs$png. You can open them directly from R using the operator !. For example:

> figs$png
[1] "figures/foo.png"
> !figs$png
[1] "figures/foo.png"

The latter call should show the PNG file using your system's PNG viewer.

Until I submit these updates to CRAN, you can install the developer's version (2.15.1.9000) as:

remotes::install_github("HenrikBengtsson/R.devices@develop")