Knitting/Rendering R Markdown Output: Can I prevent code from showing in PDF output but allow code folding in HTML output?

Question

Showing the code in PDF can be long and distracting to some readers or clients, but I would leave it as an option in the HTML version if they want to reproduce it or verify what I've done. Depending on whom I work with, I may share one or the other (or both), but I want to avoid changing the Rmd script each time to produce them.

Thus, I want to be able to knit my R Markdown script to HTML and PDF in a way so that the HTML output can show the code (with code_folding in the output: html_document options), but prevent the code from appearing in my PDF output.

Is there a way to do that without recoding part of the script each time?

Take this example R Markdown text:

---
title: "Title"
output: 
  pdf_document:
    df_print: kable
  html_document:
    code_folding: show
    df_print: paged
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```

## R Markdown

```{r mtcars}
# I want to make this code visible when I knit to HTML, but hidden when I knit to PDF. 
# How do I do that?
mtcars[1:2, 1:4]
```

It will show the mtcars chunk when it's knitted.

I can change knitr::opts_chunk$set(echo = TRUE) to knitr::opts_chunk$set(echo = FALSE) in the setup chunk to prevent the code from showing in the PDF output, but the code will disappear in the HTML output as well.

code_folding: hide can hide the code for html_document output options and allows the reader to see the code if necessary. However, code_folding: hide does not work for pdf_document output options. Is there an alternative that I can use?

Answer 1

Maybe use is_html_output in eval and echo

---
title: "Title"
output: 
 html_document:
   code_folding: show
   df_print: paged
  pdf_document:
    df_print: kable
 ---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```

## R Markdown

```{r mtcars, eval = knitr::is_html_output(), echo = knitr::is_html_output()}
# I want to make this code visible when I knit to HTML, but hidden when    I knit to PDF. 
 # How do I do that?
 mtcars[1:2, 1:4]
 ```

-output html

-output pdf