Blank plot when using cowplot with RNotebook

[DanielReedOcean]

When using cowplot with RNotebook an additional blank plot is created before the requested plot. For example,

---
title: "R Notebook"
output: html_notebook
---

```{r}
library(cowplot)
library(ggplot2)
g <- ggplot(mtcars) + geom_point(aes(mpg, hp))
plot_grid(g,g)

produces the following:

![capture](https://user-images.githubusercontent.com/11167566/33444987-0f9da026-d5d2-11e7-8221-098adb02f0dd.PNG)
 Note that this **doesn't** happen if the file is knitted as a `html_document` rather than `html_notebook`.

[clauswilke]

Could you try the following, please? Replace this line:

plot_grid(g,g)

with these three lines:

grDevices::pdf(NULL)
plot_grid(g,g)
grDevices::dev.off()

and see if this prevents the problem. If it does, we may be able to put this workaround into the plot_grid() function.

[DanielReedOcean]

When I do that there are no plots at all. Instead, I get the following:

null device 
          1 

[clauswilke]

That's good news, because I gave you the wrong code. This should work then.

grDevices::pdf(NULL)
g2 <- plot_grid(g,g)
grDevices::dev.off()
g2

[DanielReedOcean]

Boom! No blank plot.

[clauswilke]

Yeah, I think I always need to open a null pdf device when converting plots, not just when one is already open. The problem is I vaguely remember that somebody objected to that. I think in some cases the pdf device is not available. I may just make this change and see if somebody complains.

[DanielReedOcean]

Okay, thanks for getting this figured out so quickly.

[clauswilke]

I committed a fix that should resolve the issue for you and will hopefully not introduce other pains. Can you install the github version of cowplot and see if things work now?

[DanielReedOcean]

It looks great! Thanks.

[clauswilke]

Closing this. It seems to work now.