CODEWITHSUNDEEP
rr-markdownknitrpandoc
Achim Zeileis
Achim Zeileis

Reputation: 17183

Plain code chunks for R input in knitr output

Goal

In an R/Markdown document that I want to convert to LaTeX I want to set knitr options so that the entire document uses plain code chunks for all code inputs by default. Thus, for a .Rmd document with

```{r}
x <- 1 + 1
```

I want to obtain the output

```
x <- 1 + 1
```

Using the highlight option

I had hoped that the highlight=FALSE option could be used for this but this generates text-chunks rather than plain chunks. More precisely, for the simple example above, knit() produces an R-chunk by default (i.e., with highlight = TRUE):

```r
x <- 1 + 1
```

After setting knitr::opts_chunk$set(highlight = FALSE) a text-chunk is produced:

```text
x <- 1 + 1
```

But what I would like to have a plain chunk without any special language, see above.

Combination with lang option

I can obtain what I want via

knitr::opts_chunk$set(highlight = TRUE, lang = "")

Thus, I do enable highlighting but set the lang to an empty string. This indeed yields the plain code I want to have.

There is at least one disadvantage, though (apart from the rather hacky feel of this solution). Namely, if in the same document I do want to enable highlighting in the options of one specific chunk, I have to set lang = "r" now instead of highlight = TRUE, e.g.,

```{r, lang="r"}
x <- 1 + 1
```

So I wonder whether there is a better solution for this?

Background

In older versions of pandoc (I tried 2.9.x) text-chunks were converted to {verbatim} code chunks in LaTeX output.

However, more recent versions of pandoc (I tried 2.17.x) text-chunks are converted to {Shaded} instead and only plain chunks are converted to {verbatim}.

Upvotes: 1

Views: 268

Answers (2)

Yihui Xie
Yihui Xie

Reputation: 30114

Another hacky solution is (I don't even dare to explain it):

```{r}
knitr::opts_hooks$set(highlight = function(options) {
  if (!options$highlight) {
    options$highlight = TRUE
    options$lang = ''
  }
  options
})

knitr::opts_chunk$set(highlight = FALSE)
```

```{r}
1 + 1
```

```{r, highlight=TRUE}
2 + 2
```

The language name text when highlight = FALSE is currently hard-coded in knitr, so you cannot change it: https://github.com/yihui/knitr/blob/907184f82/R/hooks-md.R#L171 I'm open to making it configurable, but I'm not sure how (I hope not to add a new chunk option for setting the language in the case of highlight = FALSE).

Upvotes: 1

CALUM Polwart
CALUM Polwart

Reputation: 537

I'm not sure I entirely understand what you want, but does this in the yaml header help?

---
output:
  html_document:
    theme: null
    highlight: null
---

Upvotes: 1

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