Code chunk font size in Rmarkdown with knitr and latex

Question

In knitr, the size option works fine in a .Rnw file, the following code generates:

\documentclass{article}

\begin{document}

<<chunk1, size="huge">>=
summary(mtcars)
@


\end{document}

However, I can't get it to work in Rmarkdown. The following code does not change the font size, as it did in .rnw file. The same thing happens when trying to set options with opts_chunk$set(size="huge").

Is this the expected behavior? How does one change the chunk code font size? (I mean using knitr options, not by adding \huge before the code)

---
title: "Untitled"
output: pdf_document
---

```{r, size="huge"}
summary(mtcars)
```

I am using RStudio Version 0.98.987, knitr 1.6 and rmarkdown 0.2.68.

Answer 1

Picking up the idea to alter a knitr hook we can do the following:

def.chunk.hook  <- knitr::knit_hooks$get("chunk")
knitr::knit_hooks$set(chunk = function(x, options) {
  x <- def.chunk.hook(x, options)
  ifelse(options$size != "normalsize", paste0("\n \\", options$size,"\n\n", x, "\n\n \\normalsize"), x)
})

This snippet modifies the default chunk hook. It simply checks if the chunk option size is not equal to its default (normalsize) and if so, prepends the value of options$size to the output of the code chunk (including the source!) and appends \\normalsize in order to switch back.

So if you would add size="tiny" to a chunk, then all the output generated by this chunk will be printed that way.

All you have to do is to include this snippet at the beginning of your document.