# progressr: Render 'knitr' Documents

When compiling ("knitting") a knitr-based vignette, for instance, via `knitr::knit()`, knitr shows the progress of code chunks processed thus far using a progress bar. We can use progressr also for this type of progress reporting. To have knitr report on progress via progressr, set R option `knitr.progress.fun` as:

    options(knitr.progress.fun = function(total, labels) {
      p <- progressr::progressor(total, on_exit = FALSE)
      list(
        update = function(i) p(sprintf("chunk: %s", labels[i])),
        done = function() p(type = "finish")
      )
    })

That's it! With the above `knitr.progress.fun` option set, try to knit a document, e.g.

    progressr::handlers(global = TRUE)
    infile <- system.file("examples", "knitr-minimal.Rnw", package = "knitr")
    outfile <- knitr::knit(infile)

To customize the progress bar, try for instance:

    options(crayon.enabled = TRUE)  ## force use of colors
    progressr::handlers("pbcol", global = TRUE)

This will produce a colored progress bar in the terminal.

Comment: If the above knit example completes too quickly for you to see the progress updates, you can add the "slowdown" handler to slow down the knitting process, e.g.

    progressr::handlers(c("pbcol", "slowdown"))

This will cause the overall process to take at least ten seconds (default).

To make knitr report via progressr in all your R session, set the above R option in your `~/.Rprofile` startup file, e.g.

    if (requireNamespace("progressr", quietly = TRUE)) {
      options(knitr.progress.fun = function(total, labels) {
        p <- progressr::progressor(total, on_exit = FALSE)
        list(
          update = function(i) p(sprintf("chunk: %s", labels[i])),
          done = function() p(type = "finish")
        )
      })
    }