How do you create a progress bar when using the “foreach()” function in R?

Question

there are some informative posts on how to create a counter for loops in an R program. However, how do you create a similar function when using the parallelized version wit

Answer 1

You save the start time with Sys.time() before the loop. Loop over rows or columns or something which you know the total of. Then, inside the loop you can calculate the time ran so far (see difftime), percentage complete, speed and estimated time left. Each process can print those progress lines with the message function. You'll get an output something like

1/1000 complete @ 1 items/s, ETA: 00:00:45
2/1000 complete @ 1 items/s, ETA: 00:00:44

Obviously the looping order will greatly affect how well this works. Don't know about foreach but with multicore's mclapply you'd get good results using mc.preschedule=FALSE, which means that items are allocated to processes one-by-one in order as previous items complete.