Why no colSDs etc

If there is a fn "colMeans" why isn't there a "colSDs" etc

I think there should be, but I suppose it's a tradeoff between convenience and
"function creep".  In any case, here's an implementation that uses the existing
(fast) functions, is reasonably compatible with the S-Plus versions, and gives
the same results as "apply":


colVars <- function(x, na.rm=FALSE, dims=1, unbiased=TRUE, SumSquares=FALSE,
                    twopass=FALSE) {
  if (SumSquares) return(colSums(x^2, na.rm, dims))
  N <- colSums(!is.na(x), FALSE, dims)
  Nm1 <- if (unbiased) N-1 else N
  if (twopass) {x <- if (dims==length(dim(x))) x - mean(x, na.rm=na.rm) else
                     sweep(x, (dims+1):length(dim(x)), colMeans(x,na.rm,dims))}
  (colSums(x^2, na.rm, dims) - colSums(x, na.rm, dims)^2/N) / Nm1
}
rowVars <- function(x, na.rm=FALSE, dims=1, unbiased=TRUE, SumSquares=FALSE,
                    twopass=FALSE) {
  if (SumSquares) return(rowSums(x^2, na.rm, dims))
  N <- rowSums(!is.na(x), FALSE, dims)
  Nm1 <- if (unbiased) N-1 else N
  if (twopass) {x <- if (dims==0) x - mean(x, na.rm=na.rm) else
                     sweep(x, 1:dims, rowMeans(x,na.rm,dims))}
  (rowSums(x^2, na.rm, dims) - rowSums(x, na.rm, dims)^2/N) / Nm1
}
colStdevs <- function(x, ...) sqrt(colVars(x, ...))
rowStdevs <- function(x, ...) sqrt(rowVars(x, ...))

-- David Brahm (brahm at alum.mit.edu)
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