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

The problem is that the for-loop in R is treated special. A normal function is not allowed to look like that. Some small tweaks can make it loop pretty close though. And as @Aaron mentioned, the foreach package's %dopar% paradigm seems like the best fit. Here's my version of how it could work:

`%doprogress%` <- function(forExpr, bodyExpr) {
   forExpr <- substitute(forExpr)
   bodyExpr <- substitute(bodyExpr)

   idxName <- names(forExpr)[[2]]
   vals <- eval(forExpr[[2]])

   e <- new.env(parent=parent.frame())

   pb <- tkProgressBar(title = "Working hard:", min = 0, max = length(vals), width = 300)
   for (i in seq_along(vals)) {
     e[[idxName]] <- vals[[i]]
     eval(bodyExpr, e)
     setTkProgressBar(pb, i, label=paste( round(i/length(vals)*100, 0), "% ready!"))
   }
}


# Example usage:

foreach(x = runif(10)) %doprogress% { 
  # do something
  if (x < 0.5) cat("small\n") else cat("big")
}

As you can see, you have to type x = 1:10 instead of x in 1:10, and the infix operator %% is needed to get hold of the looping construct and the loop body. I currently don't do any error checking (to avoid muddling the code). You should check the name of the function ("foreach"), the number of arguments to it (1) and that you actually get a valid loop variable ("x") and not an empty string.