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

I tried to define a function my.render(), which preprocesses the Rmd file, and depending on the commentout argument, either keeps the HTML commenting code (TRUE) in the Rmd file or removes them (FALSE). Then writes the preprocessed Rmd file into tmp.Rmd, and uses the usual render() function.

my.render <- function(input, commentout=FALSE, ...) {
  if (commentout == FALSE) {
    ## Delete the HTML comment lines from code
    txt <- readLines(input)
    txt[grepl(" * *", txt)] <- ""
    write.table(txt, file="tmp.Rmd", sep="\n", quote=FALSE, row.names=FALSE, col.names=FALSE)
    render("tmp.Rmd", output_file=sub("Rmd","html",input), ...)
  } else {
    render(input, output_file=sub("Rmd","html",input), ...)
  }
}

It seemed to work. E.g.