How to Add CSS Classes to Individual Code Chunks in RMarkdown?

Adding CSS Classes to Individual Code Chunks in RMarkdown

In RMarkdown, customizing the appearance of code chunks can enhance document readability and aesthetics. One way to achieve this is by assigning CSS classes to specific code chunks.

Challenge:

As an RMarkdown user, you may encounter the need to add a CSS class to a certain code chunk, designated by a label, e.g., .myClass. The goal is to find a straightforward solution that does not require cumbersome workarounds like wrapping the chunk in an additional

.

Initial Attempt:

One might try using the following syntax to add the .myClass class to the code chunk labeled 'cars':

summary(cars)

Unfortunately, this approach does not work. To address this limitation, we present two solutions:

Solution 1: Knitr's class.source Option

knitr, the underlying R package for RMarkdown, recently introduced the class.source option, which allows you to specify a CSS class to the source code chunk:

summary(cars)

This method is straightforward and will add the .myClass class to the

 element surrounding the code chunk in the generated HTML document.<p><strong>Solution 2: Pandoc's fenced_code_attributes Extension and Output Hook</strong></p><p>Before knitr implemented the class.source option, a solution involving Pandoc's fenced_code_attributes extension and a custom knitr output hook was popular. This approach works by adding attributes to the </p><pre class="brush:php;toolbar:false"> tag:<pre class="brush:php;toolbar:false">---
title: "Untitled"
output:
  html_document:
    md_extensions: +fenced_code_attributes
---

knitr::knit_hooks$set(source = function(x, options) {
return(paste0(

"```{.r",
ifelse(is.null(options$class),
  "",
  paste0(" .", gsub(" ", " .", options$class))
),
"}\n",
x,
"\n```"

))
})

summary(cars)

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