Conditionally display a block of text in R Markdown

Question

I am using knitr to parse an R Markdown document . Is there a way to conditionally display a block of text in R Markdown depending on a variable in the environment I pass i

Answer 1

The solutions above may be a little clunky for larger blocks of text and not great for certain situations. Let's say I want to create a worksheet for students with some questions and also use the same .Rmd file to generate a file with solutions. I used basic LaTeX flow control:

``` {r, include = F}
# this can be e.g., in a parent .Rmd and the below can be in child
solution <- TRUE 
```
\newif\ifsol
\sol`r ifelse(solution, 'true', 'false')`

Then I can do:

What is $2 + 2$

\ifsol
4
\fi

This way you can also create alternative blocks of text using

\ifsol
Alternative 1
\else
Alternative 2
\fi