[R] sweep() and recycling

[Robin Hankin]

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