[R] How best to set library search path so user libraries come first

[Allan Engelhardt]

I want my local libraries to have priority over the system installed 
ones, which, as far as I can make out from help(".libPaths"), means they 
have to come first in that list (it doesn't actually_say_ so, but that 
seems to be the idea).

We have R_LIBS_USER which looks made for specifying where I keep my own 
libraries.  Unfortunately it comes last in .libPaths() [which appears to 
me to be a bug (1) if that means last in the search order and (2) 
because install.packages() defaults to the first element in .libPaths() 
while I think most users would (or rather: should) want to install 
packages in R_LIBS_USER most of the time].

My options for getting the order I expect seems to be

(1) Add to ~/.Rprofile a construct along the lines of:

.libPaths(c(Sys.getenv("R_LIBS_USER"), .libPaths()))

(2) Add to ~/.Renviron something like:

R_LIBS=${R_LIBS_USER}:${R_LIBS}

Both of which works but both of which seems very hackish and maybe not 
robust :-(  Is there a better way?  Am I missing how R_LIBS* are 
intended to be used?

Allan