How to make conditional block in Rmarkdown

[cderv]

A small recipe about conditional block

• using if in inline r block : `r if(test) {do}`
• using chunk option eval with a variable define

```{r conditional, eval = variable-test}
do_something()
```

Related SO question

• https://stackoverflow.com/questions/25407102/conditionally-display-a-block-of-text-in-r-markdown
• https://stackoverflow.com/questions/25354903/conditional-echo-or-eval-or-include-in-rmarkdown-chunks
• https://stackoverflow.com/questions/39550732/is-there-a-way-to-have-conditional-markdown-chunk-execution-in-rmarkdown
• https://stackoverflow.com/questions/25837990/preventing-a-chunk-run-in-rmarkdown

Related Knitr example

• https://github.com/yihui/knitr-examples/blob/master/011-conditional-eval.Rnw

[cderv]

Very interesting use case based on this : apply eval = TRUE based on the name (label) of the chunk
https://stackoverflow.com/questions/26993254/how-to-get-chunk-name-in-knitr

An opportunity to show opts_current$get("label") but there seems to be a question about the execution order of the chunk. 🤔

[cderv]

I did not know this was also possible with Latex (see the knitr example)

\documentclass{article}
\newif\ifmyboolean
\begin{document}

<<setup>>=
myboolean='true' # or set it to 'false'
@
% assign true or false to myboolean
\myboolean\Sexpr{myboolean}

\ifmyboolean
hello, foo!
\else
hey, bar!
\fi

\end{document}

[cderv]

Some recipes already added:

• a068891 about block conditional to package
• aa37cb1 about asis engine for conditional text in Rmd.

[cderv]

Related to #113

I think we can add more recipes based on examples in questions for conditional execution or echoing of chunks.

Conditional include example already shown with output function : https://bookdown.org/yihui/rmarkdown-cookbook/latex-html.html

[yihui]

I think these are special cases or applications of https://bookdown.org/yihui/rmarkdown-cookbook/chunk-variable.html so we can probably close this one.