On Jun 20, 2005, at 04:58 pm, Prof Brian Ripley wrote:
> The issue here is that the equivalent command array(1:5, c(6,6)) (to
> matrix(1:5,6,6)) gives no warning, and sweep uses array().
>
> I am not sure either should: fractional recycling was normally allowed
> in S3 (S4 tightened up a bit).
>
> Perhaps someone who thinks sweep() should warn could contribute a
> tested patch?
>
OK, modified R code and Rd file below (is this the best way to do
this?)
"sweep" <-
function (x, MARGIN, STATS, FUN = "-", give.warning = FALSE, ...)
{
FUN <- match.fun(FUN)
dims <- dim(x)
if(give.warning & length(STATS)>1 & any(dims[MARGIN] !=
dim(as.array(STATS)))){
warning("array extents do not recycle exactly")
}
perm <- c(MARGIN, (1:length(dims))[-MARGIN])
FUN(x, aperm(array(STATS, dims[perm]), order(perm)), ...)
}
\name{sweep}
\alias{sweep}
\title{Sweep out Array Summaries}
\description{
Return an array obtained from an input array by sweeping out a summary
statistic.
}
\usage{
sweep(x, MARGIN, STATS, FUN="-", give.warning = FALSE, \dots)
}
\arguments{
\item{x}{an array.}
\item{MARGIN}{a vector of indices giving the extents of \code{x}
which correspond to \code{STATS}.}
\item{STATS}{the summary statistic which is to be swept out.}
\item{FUN}{the function to be used to carry out the sweep. In the
case of binary operators such as \code{"/"} etc., the function name
must be quoted.}
\item{give.warning}{Boolean, with default \code{FALSE} meaning to
give no warning, even if array extents do not match. If
\code{TRUE}, check for the correct dimensions and if a
mismatch is detected, give a suitable warning.}
\item{\dots}{optional arguments to \code{FUN}.}
}
\value{
An array with the same shape as \code{x}, but with the summary
statistics swept out.
}
\note{
If \code{STATS} is of length 1, recycling is carried out with no
warning irrespective of the value of \code{give.warning}.
}
\references{
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
\emph{The New S Language}.
Wadsworth \& Brooks/Cole.
}
\seealso{
\code{\link{apply}} on which \code{sweep} used to be based;
\code{\link{scale}} for centering and scaling.
}
\examples{
require(stats) # for median
med.att <- apply(attitude, 2, median)
sweep(data.matrix(attitude), 2, med.att)# subtract the column medians
a <- array(0, c(2, 3, 4))
b <- matrix(1:8, c(2, 4))
sweep(a, c(1, 3), b, "+", give.warning = TRUE) # no warning:
all(dim(a)[c(1,3)] == dim(b))
sweep(a, c(1, 2), b, "+", give.warning = TRUE) # warning given
}
\keyword{array}
\keyword{iteration}
--
Robin Hankin
Uncertainty Analyst
National Oceanography Centre, Southampton
European Way, Southampton SO14 3ZH, UK
tel 023-8059-7743
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