4D Pie Charts

There are some pieces of code that are so simple and obvious that they really ought to be included in base R somewhere.

Geometric mean and standard deviation – a staple for anyone who deals with lognormally distributed data.

geomean <- function(x, na.rm = FALSE, trim = 0, ...)
{
   exp(mean(log(x, ...), na.rm = na.rm, trim = trim, ...))
}

geosd <- function(x, na.rm = FALSE, ...) 
{
   exp(sd(log(x, ...), na.rm = na.rm, ...))
}

A drop option for nlevels. Sure your factor has 99 levels, but how many of them actually crop up in your dataset?

nlevels <- function(x, drop = FALSE) base::nlevels(x[, drop = drop])

A way of converting factors to numbers that is quicker than as.numeric(as.character(my_factor)) and easier to remember than the method suggested in the FAQ on R.

factor2numeric <- function(f)
{
   if(!is.factor(f)) stop("the input must be a factor")
   as.numeric(levels(f))[as.integer(f)]
}

A “not in” operator. Not many people know the precedence rules well enough to know that !x %in% y means !(x %in% y) rather than (!x) %in% y, but x %!in% y should be clear to all.

"%!in%" <- function(x, y) !(x %in% y)

I’m sure there are loads more snippets like this that would be useful to have; please contribute your own in the comments.

EDIT:
Thanks for all your suggestions. I had another idea while drifting off to sleep last night. The error message thrown by stopifnot is a little clunky, which means that I end up with lots of instances of if(!some_condition) stop("A nicer error message"). The factor2numeric function above is typical. If stopifnot allowed for custom error messages, I’d be much more inclined to use it.

stopifnot <- function (..., errmsg = NULL) 
{
    n <- length(ll <- list(...))
    if (n == 0L) 
        return(invisible())
    mc <- match.call()
    for (i in 1L:n) if (!(is.logical(r <- ll[[i]]) && !any(is.na(r)) && 
        all(r))) {
        ch <- deparse(mc[[i + 1]], width.cutoff = 60L)
        if (length(ch) > 1L) 
            ch <- paste(ch[1L], "....")
        if(is.null(errmsg)) errmsg <- paste(ch, " is not ", if (length(r) > 1L) 
            "all ", "TRUE", sep = "")
        stop(errmsg, call. = FALSE)
    }
    invisible()
}

ANOTHER EDIT:
Once you start thinking about this, it’s really easy to keep coming up with ideas. Checking to see if an object is scalar is easy – it just has to have length 1.

is.scalar <- function(x) length(x) == 1