In "R News", in "Changes in R 3.3.0", in "New
Features", a news item is
match.arg(arg) (the one-argument case) is faster; so is sort.int(). (PR#16640)
While it was motivated by speeding up tapply, it is in a separate bug number:
16652 (https://bugs.r-project.org/bugzilla3/show_bug.cgi?id=16652).