Add markdown code chunk to R Markdown document

4
votes

I would like to write an R Markdown document which presents code examples of how to write an R Markdown document. For example, I want to show in the document how to render text as bold.

`**this is bold**` will render 'this is bold' with bold text, i.e. **this is bold**

That works fine, the ` render the text within as code. However, I can't figure out how to get a code chunk to display properly. e.g.

```{markdown, eval=FALSE}
  ```{r}
  x = rnorm(1)
  ```
```

This doesn't work because markdown isn't a supported language. I can't enclose the r code block in ` because I need that symbol to mark the beginning of the code chunk and it only works inline.

I can do some hoop jumping by actually using R

```{r, echo="FALSE"}
o = "```{r}\nx=sample(1)\n```\n"
cat(o)
```

which renders as 

## ```{r}
## x=sample(1)
## ```

But this is more complicated for me writing the document and the code it generates doesn't allow for simple copy/paste.

Is there a native way to render as code the markdown necessary to create the R code block?

3
r-markdownknitr
knitr FAQ 7: yihui.name/knitr/faq – Yihui Xie
@YihuiXie you could be interested in reading Mark's answer, it could deserve a place in your FAQ – Dan Chaltiel
@DanChaltiel Thanks! I've read Mark's answer when it was posted. The knitr FAQ 7 provided essentially the same solution, though. – Yihui Xie

3 Answers

4
votes

I found the bookdown book on Rmarkdown which has examples of R code chunks being rendered via Rmarkdown. The book source is available on GitHub and the relevant chapter is located here.

The chunk below works as desired. I can't explain why the `r ''` is required at the beginning of the block, but it is. 

````markdown
`r ''````{r}
x = sample(1)
```
````
1
votes

If you don't put {r} after the three backticks, rmarkdown will just pass the block on to markdown and it almost works. For example, this

```
  ```{r}
  x = rnorm(1)
  ```
```

displays as

screenshot

It's not quite right; the braces around the r have been removed. (I think r-markdown did that, not markdown.) I don't know if there's an option to force them in, but they will appear if there's a non-letter ahead of the r. You can put in a space, or (if you can figure out how) a zero width space, which R will display using "\u200B".

1
votes

You can use the experimental knitrhooks package, which adds the chunk option chunk_head to enable us to keep the header. The package is in development on GitHub here.

To install the package, use the command devtools::install_github("nathaneastwood/knitrhooks"). Once installed, you can use the chunk hook by loading the package and then calling the function chunk_head() in your header.

Here is an example:

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

```{r, include = FALSE}
library(knitrhooks)
chunk_head()
```


```{r, chunk_head = TRUE, echo = TRUE}
x <- sample(1)
```

enter image description here

Unfortunately, this will not display syntax highlighting, but as discussed within this issue, this is a limitation within how knitr processes the file.