Promote your favorite R functions

The 27 base and recommended libraries of the standard R 2.12 distribution together contain 3556 functions (you can check using the code posted after the jump). Many of the functions are commonly used: c, data.frame, rnorm, lm. But some of those functions, while being extremely useful, may be less well known to many R users. Some examples I'd wish I'd learned about earlier include tapply, agrep, and formatC. There are also several really useful help pages that aren't associated with specific functions at all, like Syntax and .Machine, that don't get the exposure they deserve.

To help get some of these "hidden gems" of the R documentation better known, we've added a "Function of the Day" section to the home page of inside-R.org. What R functions and help pages do you wish you'd known about earlier? Add a comment to your favorite pages in the Language Reference explaining why they deserve more love, and we'll consider the comments nominations for the Function of the Day.

inside-R.org: Language Reference

# list of base and recommended packages in R 2.12
base.rec <- c(
 "base","boot","class","cluster","codetools",
 "datasets","foreign","graphics","grDevices",
 "grid","KernSmooth","lattice","MASS",
 "Matrix","methods","mgcv","nlme",
 "nnet","rpart","spatial","splines",
 "stats","stats4","survival","tcltk",
 "tools","utils") 
n.obj <- rep(0, length(base.rec))
names(n.obj) <- base.rec
 
# count objects in each package
for(p in base.rec) {
	require(p,character.only=TRUE)
	n.obj[p] <- length(
	  objects(name=paste("package",p,sep=":")))
	}
 
# total count
sum(base.rec)