Every once in while I have to write a function that contains a loop doing thousands or millions of calculations. To make sure that the function does not get stuck in an endless loop or just to fulfill the human need of control it is useful to monitor the progress. So  first I tried the following:

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total <- 10
for(i in 1:total){
   print(i)
   Sys.sleep(0.1)
}

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Unfortunately this does not work as the console output to the basic R GUI is buffered. This means that it is printed to the console at once after the loop is finished. The R FAQs (7.1) explains a solution: Either to change the R GUI buffering settings in the Misc menu which can be toggled via or to tell R explicitly to empty the buffer by flush.console(). So like this it works:

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total <- 20
for(i in 1:total){
   Sys.sleep(0.1)
   print(i)
   # update GUI console
   flush.console()                          
}

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Of course it would be even nicer to have a real progress bar. For different progress bars we can use the built-in R.utils package. First a text based progress bar:

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

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To get a GUI progress bar the tkProgressBar() function from the tcltk package can used.

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total <- 20
# create progress bar
pb <- tkProgressBar(title = "progress bar", min = 0,
                    max = total, width = 300)

for(i in 1:total){
   Sys.sleep(0.1)
   setTkProgressBar(pb, i, label=paste( round(i/total*100, 0),
                                        "% done"))
}
close(pb)

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Last but not least, a progress bar using the Windows operating system.

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# create progress bar
pb <- winProgressBar(title = "progress bar", min = 0,
                     max = total, width = 300)

for(i in 1:total){
   Sys.sleep(0.1)
   setWinProgressBar(pb, i, title=paste( round(i/total*100, 0),
                                        "% done"))
}
close(pb)

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Ciao, Mark