Is there a way to update existing text in the R console?

Question

I am wondering if it is possible to update existing text in the R console? E.g., if I run a function that takes a bit longer to execute, I would like to know how far along it is currently.

I could achieve this by issuing print("at 10%"), print("at 20%"), etc. at appropriate locations in the function. But this could be a relatively long output, since it produces a new line each time.

Is there a way to update the console text from the running function in a way that it updates the current line in the console and not create a new line? E.g. >at 10% in the console changes to >at 20% when appropriate.

Answer 1

Flushing the console works but may cause flickering. If you want a very simple text line update, then it’s sufficient to go back to the beginning of the line by printing \r and to overwrite the text there.

Here’s a progress function from the rcane module:

progress <- function (x, max = 100) {
    percent <- x / max * 100
    cat(sprintf('\r[%-50s] %d%%',
                paste(rep('=', percent / 2), collapse = ''),
                floor(percent)))
    if (x == max)
        cat('\n')
}

Here’s a screenshot of the progress bar in action:

And finally, this can be wrapped nicely so that its usage is effortless:

map_with_progress(some_function, some_data)

(See the link above for an implementation; of course R’s own txtprogressBar is quite a bit more flexible.)

Answer 2

Although a general answer to the question of "is it possible to update text in R console" was not given, it is not necessary for my particular problem. The progress bars mentioned by Ananda and Dason in comments to my questions are a solution to the problem of tracking the status of an executing function. (Updating text would actually probably not make sense in this case, if at all possible, since sometimes there is other output from the functions, which could "hide" the updated text.)

Examples of how to implemented different progress bars are well described at: http://www.r-bloggers.com/r-monitoring-the-function-progress-with-a-progress-bar/

For completeness, a slightly updated example from above mentioned link of the txtProgressBar() (which works at least with Windows+RStudio):

total <- 20
# create progress bar
pb <- txtProgressBar(min = 0, max = total, style = 3)
for(i in 1:total){
  Sys.sleep(0.1)
  print("Result XZY")
  # update progress bar      
  setTxtProgressBar(pb, i)
}
close(pb)