[R] Reset R's library to base packages only (remove all installed contributed packages)

[Janko Thyson]

Dear list,

is there a way to comfortably "reset" R's library such that it only 
contains only the base packages again? In other words, how can I 
uninstall all contributed packages that I installed? Is there some sort 
of index that's keeping track of what has been installed? If so, a 
pointer would be great.

AFAIU, if you don't create such an "index file" yourself and loose track 
of what you installed, probably the best way to "reset" R is to actually 
re-install it. That's exactly what I'm trying to avoid.

I would like something like

path.lib <- "path/to/R/lib"
pkgs.to.remove <- readLines(path.to.index.file)
sapply(pkgs.to.remove, uninstall.packages, lib=path.lib)

Best regards,
Janko