[Rd] sweep sanity checking?

From: Ben Bolker <bolker_at_zoo.ufl.edu>
Date: Fri, 29 Jun 2007 17:29:36 -0400

  A friend of mine just got bitten by the fact that sweep() will happily sweep out a STATS vector of an arbitrary length -- even one whose length is not a divisor of any of the margins -- without complaining. I know the answer to this could be "well just don't do that", but it's easy to make a mistake in which margin you're sweeping ...

  What would R-core think of the following 'enhanced' sweep? It always warns if dim(x)[MARGIN] is not a multiple of length(STATS) {it's very hard indeed for me to think of a situation where you'd actually want this}; if check.margin=TRUE it is a bit stricter, complaining whenever dim(x)[MARGIN] doesn't match length(STATS).

  This change seems fairly harmless since it never does anything more than warn; the default for check.margin could be FALSE if you wanted to allow people a bit more rope to hang themselves with ... (of course this won't prevent you from sweeping the wrong margin of a square matrix, but nothing will).

    Ben Bolker

sweep <- function (x, MARGIN, STATS, FUN = "-", check.margin=TRUE, ...) {

    FUN <- match.fun(FUN)
    dims <- dim(x)
    if (check.margin && dims[MARGIN]!=length(STATS)) {       warning("length(STATS) != dim(x)[MARGIN]")     } else if (dims[MARGIN] %% length(STATS)!=0)       warning("dim(x)[MARGIN] is not a multiple of length(STATS)")     perm <- c(MARGIN, (1:length(dims))[-MARGIN])     FUN(x, aperm(array(STATS, dims[perm]), order(perm)), ...)   }

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