this hastily written script converts an R script which starts with a comment into a Rmd file, splitting code into chunks and turning comments into text

script2Rmd

script2Rmd <- function(filein) {
  lns <- scan(filein,what="char",sep="\n")
  comments <- substr(lns,1,1) == "#"
  lnsout <- lns
  lnsout[comments] <- substr(lns[comments],3,nchar(lns[comments]))
  rlelens <- rle(comments)$lengths
  f <- factor(rep(seq_along(rlelens),rlelens))
  lnsoutsplit <- split(lnsout, f)
  chunkdelims <- rep(c("\n\n```{r}","```\n\n"), length(lnsoutsplit)/2)
  #from https://stat.ethz.ch/pipermail/r-help/2006-March/101023.html
  interleave <- function(v1,v2)
  {
    ord1 <- 2*(1:length(v1))-1
    ord2 <- 2*(1:length(v2))
    c(v1,v2)[order(c(ord1,ord2))]
  }
  lnsoutchunked <- interleave(lnsoutsplit,chunkdelims)
  write(do.call(c,lnsoutchunked), file=paste0(filein,"md"))
}

I just learned this is similarly done by knitr::spin