In R, do an operation temporarily using a setting such as working directory

Question

I'm almost certain I've read somewhere how to do this. Instead of having to save the current option (say working directory) to a variable, change the w.d, do an operation, and then revert back to what it was, doing this inside a function akin to "with" relative to attach/detach. A solution just for working directory is what I need now, but there might be a more generic function that does that sort of things? Or ain't it?

So to illustrate... The way it is now:

curdir <- getwd()
setwd("../some/place")
# some operation
setwd(curdir)

The way it is in my wildest dreams:

with.dir("../some/place", # some operation)

I know I could write a function for this, I just have the impression there's something more readily available and generalizable to other parameters too.

Thanks

Answer 1

There is an idiom for this in some of R's base plotting functions

op <- par(no.readonly = TRUE)

# par(blah = stuff)
# plot(stuff)

par(op)

that is so unbelievably crude as to be fully portable to options() and setwd().

Fortunately it's also easy to implement a crude wrapper:

with_dir <- function(dir, expr) {
    old_wd <- getwd()
    setwd(dir)
    result <- evalq(expr)
    setwd(old_wd)
    result
}

I'm no wizard with nonstandard evaluation so evalq could be unstable somehow. More on NSE in an old write-up by Lumley and also in Wickham's Advanced R, but it's dense stuff and I haven't wrapped my head around it all yet.

edit: as per Ben Bolker's comment, it's probably better to use on.exit for this:

with_dir <- function(dir, expr) {
    old_wd <- getwd()
    on.exit(setwd(old_wd))
    setwd(dir)
    evalq(expr)
}

From the R docs:

on.exit records the expression given as its argument as needing to be executed when the current function exits (either naturally or as the result of an error). This is useful for resetting graphical parameters or performing other cleanup actions.