Useful little functions in R?

What are the functions that you wrote, don't quite deserve a package, but you wish to share?

I will throw in some of mine:

destring <- function(x) {
    ## convert factor to strings
    if (is.character(x)) {
        as.numeric(x)
    } else if (is.factor(x)) {
        as.numeric(levels(x))[x]
    } else if (is.numeric(x)) {
        x
    } else {
        stop("could not convert to numeric")
    }
}

pad0 <- function(x,mx=NULL,fill=0) {
  ## pad numeric vars to strings of specified size
  lx <- nchar(as.character(x))
  mx.calc <- max(lx,na.rm=TRUE)
  if (!is.null(mx)) {
    if (mx<mx.calc) {
      stop("number of maxchar is too small")
    }
  } else {
    mx <- mx.calc
  }
  px <- mx-lx
  paste(sapply(px,function(x) paste(rep(fill,x),collapse="")),x,sep="")
}


.eval <- function(evaltext,envir=sys.frame()) {
  ## evaluate a string as R code
  eval(parse(text=evaltext), envir=envir)
}

## trim white space/tabs
## this is marek's version
trim<-function(s) gsub("^[[:space:]]+|[[:space:]]+$","",s)