A basic previewer for R Markdown files edited with Emacs

.emacs

(add-to-list 'auto-mode-alist '("\\.md\\'" . markdown-mode))
(add-to-list 'auto-mode-alist '("\\.Rmd\\'" . markdown-mode))
(add-to-list 'auto-mode-alist '("\\.rmd\\'" . markdown-mode))
(add-hook 'markdown-mode-hook 'turn-on-outline-minor-mode)

(defun rmarkdown-new-chunk (name)
  "Insert a new R chunk."
  (interactive "sChunk name: ")
  (insert "\n```{r " name "}\n")
  (save-excursion
    (newline)
    (insert "```\n")
    (previous-line)))

(defun rmarkdown-weave-file ()
  "Run knitr on the current file and weave it as MD and HTML."
  (interactive)
  (shell-command 
   (format "knit.sh -c %s" 
       (shell-quote-argument (buffer-file-name)))))

(defun rmarkdown-tangle-file ()
  "Run knitr on the current file and tangle its R code."
  (interactive)
  (shell-command 
   (format "knit.sh -t %s" 
       (shell-quote-argument (buffer-file-name)))))

(defun rmarkdown-preview-file ()
  "Run knitr on the current file and display output in a browser."
  (interactive)
  (shell-command 
   (format "knit.sh -b %s" 
       (shell-quote-argument (buffer-file-name)))))

knit.sh

#! /usr/bin/env sh

#
# Process R Markdown file and display HTML output directly in the browser.
#

usage()
{
cat << EOF
Usage: $0 [-h] [-c] [-b] [-t] filename

This script weaves and tangles an R Markdown file using knitr.

OPTIONS:
   -h      show this message
   -c      compile Rmd file to Markdown and HTML
   -b      compile Rmd file and display HTML file in browser
   -t      tangle Rmd file
EOF
}

while getopts ":hcbt" o; do
    case $o in
	h)
	    usage
	    exit 1
	    ;;
	c)
	    compile=1
	    ;;
	b) 
	    browser=1
	    ;;
	t)    
	    tangle=1
	    ;;
	*)
	    usage
	    ;;
    esac
done
shift $((OPTIND-1))

if [ -r "$1" ]; then
    mdfile="$1"
    mdfile="${mdfile%.*}"  # remove extension
    if [[ $compile = 1 ]]; then
	(
	    Rscript -e "require(knitr); require(markdown); knit('${mdfile}.rmd', quiet=TRUE); \
                        markdownToHTML('${mdfile}.md', '${mdfile}.html')"
	) > /dev/null 2>&1
    fi
    if [[ $browser = 1 ]]; then
	(
	    Rscript -e "require(knitr); require(markdown); knit('${mdfile}.rmd', quiet=TRUE); \
                        markdownToHTML('${mdfile}.md', '${mdfile}.html'); browseURL('${mdfile}.html')"
	) > /dev/null 2>&1
    fi
    if [[ $tangle = 1 ]]; then
	(
	    Rscript -e "require(knitr); purl('${mdfile}.rmd')"
	) > /dev/null 2>&1
    fi	
else
    exit 0
fi

Here is a very basic shell script to knit R Markdown file and to display output as HTML directly in the browser. I added some Elisp functions to mimic ESS ess-noweb-new-chunk (or ⌥⌘I in RStudio)--probably better than relying on custom macros--and call the shell script directly from within Emacs. Basically, we can tangle the R Markdown file, weave it or weave it and output result in the browser. No temporary files are created: Everything goes in the current working directory. Output from Rscript are also suppressed, but if you want to get information into the *Shell command output* buffer you can just suppress the redirection of stderr and stdout to /dev/null.

Of course, custom keybindings can be added to avoid typing M-x rmarkdown-new-chunk repeatedly. It is also assumed that knit.sh is executable and available in system path (chmod +x knit.sh and sudo mv knit.sh /usr/local/bin if this is not the case).

You will need markdown-mode.el, which is available from MELPA, and R knitr and markdown packages.