How to print progress bar of R function without for loop?

Question

I have a function that takes a long time to run (involves many calculations in a large dataset). I want to include a progress bar to see if it's making progress. My function has no for loops; I don't understand how to add a progress bar if I don't have a for loop in the function.

I tried adding a for loop to get the progress bar to work, but it's just printing the progress bar without doing the calculations (I believe), i.e. when I print result I get NULL:

install.packages("svMisc")
require("svMisc")

# Test function
funct<-function(a,b,c)for (i in 0:101){
  progress(i, progress.bar=TRUE)
  Sys.sleep(0.01)
  x<-a*a
  y<-x+b
  z<-y/2
  if (i == 101) message("Done!")
}

result <- funct(-2.6e+70,-2.5e+121,6)
result

Feel free to suggest something other than svMisc.

question from:https://stackoverflow.com/questions/65598437/how-to-print-progress-bar-of-r-function-without-for-loop

Answer 1

In general, reporting the progress of a function will require a loop (or possibly a number of lines of code), as you've set out in your example. Your example is performing the calculations, it is just not returning them - remember that R functions return the value of the last calculation unless there is an explicit return() statement. In this case, the message() function returns NULL.

The minor modification to your code below demonstrates the expected behaviour of the progress bar, followed by result having the calculated value.

install.packages("svMisc")
require("svMisc")

# Test function
funct<-function(a,b,c){
  for (i in 0:101){
    progress(i, progress.bar=TRUE)
    Sys.sleep(0.01)
    x<-a*a
    y<-x+b
    z<-y/2
    if (i == 101) message("Done!")
  }
  return(z)
}

result <- funct(-2.6e+70,-2.5e+121,6)

#           0%---------25%---------50%---------75%--------100%
# Progress: ||||||||||||||||||||||||||||||||||||||||||||||||||
# Done!

result

# [1] 3.38e+140