在 rstudio 中执行选定的 Markdown 块的方式（使用 knitr）

Question

Is there a way to test-out and peek at the output of a selected portion of markdown in RStudio? It seems you either run R code or have to compile the entire RMD page in order to see the output.

Answer 1

This is a Windows-only solution and it uses the clipboard instead of the current selection:

Define the following function:

preview <- function() {
  output <- tempfile(fileext = ".html")
  input <- tempfile(fileext = ".Rmd")
  writeLines(text = readClipboard(), con = input)
  rmarkdown::render(input = input, output_file = output)
  rstudioapi::viewer(output)
}

Then, copy the markdown you want to preview and run preview() . Note that the output might be different from the output in the final document because

• the code is evaluated in the current environment
• only the copied markdown is evaluated, meaning that the snippet has no context whatsoever.

---

A solution without using the clipboard will most likely employ rstudioapi::getActiveDocumentContext() . It boils down to something along the lines of a modified preview function

preview2 <- function() {
  code <- rstudioapi::getActiveDocumentContext()$selection
  # drop first line
  # compile document (as in preview())
  # stop execution (THIS is the problem)
}

which could be used by running preview() followed by the markdown to render:

preview2()
The value of pi is `r pi`.

The problem is, I don't see how the execution could be halted after calling preview2() to prevent R from trying to parse The value of … . See this related discussion .