Changing page size within Rmarkdown document - r

Question

I have a very large phylogenetic tree that I'd quite like to insert into a supplementary material I'm writing using Rmarkdown and knitr. I dislike splitting trees across pages and I doubt anybody would print this out anyway so I thought I'd just have a large page in the middle of the pdf I'm generating.
The question is how do I change page size for one page in an otherwise A4 document? I'm pretty new to knitr and I've found global paper size options but I'm struggling to find ways of setting up what would be the equivalent of sections in Word.
(Update) Hi does anybody else have a suggestion? I tried the pdfpages package but this seems to result in an equally small figure on a page the size of the pdf that is being pasted in i.e. if I make a 20in by 20in pdf figure then paste the page in using \includepdf then I get a 20in by 20in page with a much smaller figure on it (the same as the \eject example above). It seems like knitr or Latex is forcing the graphics to have a specific size regardless of page size. Any ideas? Here's a reproducible example:
---
title: "Test"
output:
pdf_document:
latex_engine: xelatex
header-includes:
- \usepackage{pdfpages}
---
```{r setup, include=FALSE}
require(knitr)
knitr::opts_chunk$set(echo = FALSE,
warning=FALSE,
message=FALSE,
dev = 'pdf',
fig.align='center')
```
```{r mtcars, echo=FALSE}
library(ggplot2)
pdf("myplot.pdf", width=20, height=20)
ggplot(mtcars, aes(mpg, wt)) + geom_point()
dev.off()
```
#Here's some text on a normal page, the following page is bigger but has a tiny figure.
\newpage
\includepdf[fitpaper=true]{myplot.pdf}

Answer 1

You should be able to use \ejectpage like this:
---
output: pdf_document
---
```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```
## R Markdown
This is an R Markdown document. Markdown is a simple formatting syntax for authoring HTML, PDF, and MS Word documents. For more details on using R Markdown see <http://rmarkdown.rstudio.com>.
When you click the **Knit** button a document will be generated that includes both content as well as the output of any embedded R code chunks within the document. You can embed an R code chunk like this:
```{r cars}
summary(cars)
```
## Including Plots
You can also embed plots, for example:
```{r pressure, echo=FALSE}
plot(pressure)
```
Note that the `echo = FALSE` parameter was added to the code chunk to prevent printing of the R code that generated the plot.
\eject \pdfpagewidth=20in \pdfpageheight=20in
```{r mtcars}
library(ggplot2)
ggplot(mtcars, aes(mpg, wt)) + geom_point()
```
\eject \pdfpagewidth=210mm \pdfpageheight=297mm
Back
(I can only remember the A4 height in mm for some reason)

Answer 2

I have just faced the same struggle when dealing with a large phylogenetic tree.
Based on hrbrmstr's answer, I came up with the snippet below.
The trick is to make knitr generate the figure but not include it in the intermediate .tex right away (hence fig.show="hide"). Then, because figure paths are predictable, you can insert it with some latex after the code chunk.
However, the new page height is not taken into account when positioning page numbers, so they tend to be printed over your image. I have tried to overcome this behavior multiple times, but in the end I simply turned them off with \thispagestyle{empty}.
---
output: pdf_document
---
```{r fig_name, fig.show="hide", fig.height=30, fig.width=7}
plot(1)
```
\clearpage
\thispagestyle{empty}
\pdfpageheight=33in
\begin{figure}[p]
\caption{This is your caption.}\label{fig:fig_name}
{\centering \includegraphics[height=30in, keepaspectratio]{main_files/figure-latex/fig_name-1} }
\end{figure}
\clearpage
\pdfpageheight=11in