Wrapper to FOR loops with progress bar

Question

I like to use a progress bar while running slow for loops. This could be done easily with several helpers, but I do like the tkProgressBar from tcl

Answer 1

My solution is very similar to Andrie's except it uses base R, and I second his comments on the need to wrap what you want to do in a function and the subsequent need to use <<- to modify stuff in a higher environment.

Here's a function that does nothing, and does it slowly:

myfun <- function(x, text) {
  Sys.sleep(0.2)
  cat("running ",x, " with text of '", text, "'\n", sep="")
  x
}

Here's my forp function. Note that regardless of what we're actually looping over, it instead loops over the sequence 1:n instead and get the right term of what we actually want within the loop. plyr does this automatically.

library(tcltk)
forp <- function(x, FUN, ...) {
  n <- length(x)
  pb <- tkProgressBar(title = "Working hard:", min = 0, max = n, width = 300)
  out <- vector("list", n)
  for (i in seq_len(n)) {
    out[[i]] <- FUN(x[i], ...)
    setTkProgressBar(pb, i, label=paste( round(i/n*100, 0), "% ready!"))
  }
  close(pb)
  invisible(out)
}

And here's how both for and forp might be used, if all we want to do is call myfun:

x <- LETTERS[1:5]
for(xi in x) myfun(xi, "hi")
forp(x, myfun, text="hi")

And here's how they might be used if we want to modify something along the way.

out <- "result:"
for(xi in x) {
  out <- paste(out, myfun(xi, "hi"))
}

out <- "result:"
forp(x, function(xi) {
    out <<- paste(out, myfun(xi, "hi"))
})

For both versions the result is

> out
[1] "result: A B C D E"

EDIT: After seeing your (daroczig's) solution, I have another idea that might not be quite so unwieldy, which is to evaluate the expression in the parent frame. This makes it easier to allow for values other than i (now specified with the index argument), though as of right now I don't think it handles a function as the expression, though just to drop in instead a for loop that shouldn't matter.

forp2 <- function(index, x, expr) {
  expr <- substitute(expr)
  n <- length(x)
  pb <- tkProgressBar(title = "Working hard:", min = 0, max = n, width = 300)
  for (i in seq_len(n)) {
    assign(index, x[i], envir=parent.frame())
    eval(expr, envir=parent.frame())
    setTkProgressBar(pb, i, label=paste( round(i/n*100, 0), "% ready!"))
  }
  close(pb)
}

The code to run my example from above would be

out <- "result:"
forp2("xi", LETTERS[1:5], {
    out <- paste(out, myfun(xi, "hi"))
})

and the result is the same.

ANOTHER EDIT, based on the additional information in your bounty offer:

The syntax forX(1:1000) %doX$ { expression } is possible; that's what the foreach package does. I'm too lazy right now to build it off of your solution, but building off mine, it could look like this:

`%doX%` <- function(index, expr) {
  x <- index[[1]]
  index <- names(index)
  expr <- substitute(expr)
  n <- length(x)
  pb <- tkProgressBar(title = "Working hard:", min = 0, max = n, width = 300)
  for (i in seq_len(n)) {
    assign(index, x[i], envir=parent.frame())
    eval(expr, envir=parent.frame())
    setTkProgressBar(pb, i, label=paste( round(i/n*100, 0), "% ready!"))
  }
  close(pb)
  invisible(out)
}

forX <- function(...) {
  a <- list(...)
  if(length(a)!=1) {
    stop("index must have only one element")
  }
  a
}

Then the use syntax is this, and the result is the same as above.

out <- "result:"
forX(xi=LETTERS[1:5]) %doX% {
  out <- paste(out, myfun(xi, "hi"))
}
out