From: Heather Turner <Heather.Turner_at_warwick.ac.uk>

Date: Wed 22 Jun 2005 - 01:33:20 EST

Date: Wed 22 Jun 2005 - 01:33:20 EST

The first example is a natural use of recycling. E.g.

sweep(matrix(1:100, 50, 2), 1, c(1, 1000), "+", give.warning = TRUE)

sweep(matrix(1:100, 50, 2), 1, rep(c(1, 1000), 25), "+", give.warning = TRUE)

>>> Robin Hankin <r.hankin@noc.soton.ac.uk> 06/21/05 02:47pm >>>

Hi

On Jun 21, 2005, at 02:33 pm, Heather Turner wrote:

> I think the warning condition in Robin's patch is too harsh - the

*> following examples seem reasonable to me, but all produce warnings
**>
**> sweep(array(1:24, dim = c(4,3,2)), 1, 1:2, give.warning = TRUE)
**> sweep(array(1:24, dim = c(4,3,2)), 1, 1:12, give.warning = TRUE)
**> sweep(array(1:24, dim = c(4,3,2)), 1, 1:24, give.warning = TRUE)
**>
*

The examples above do give warnings (as intended) but I think all three
cases above

are inimical to the spirit of sweep(): nothing is being "swept" out.

So a warning is appropriate, IMO.

In any case, one can always suppress (or ignore!) a warning if one knows
what one is doing. YMMV, but if I wanted to do the above operations I
would

replace

sweep(array(0, dim = c(4,3,2)), c(1,3), 1:12, "+" , give.warning =
**FALSE)
**
with

aperm(array(1:12,c(4,2,3)),c(1,3,2))

best wishes

rksh

> I have written an alternative (given below) which does not give

*> warnings in the above cases, but does warn in the following case
**>
**>> sweep(array(1:24, dim = c(4,3,2)), 1:2, 1:3)
**> , , 1
**>
**> [,1] [,2] [,3]
**> [1,] 0 3 6
**> [2,] 0 3 9
**> [3,] 0 6 9
**> [4,] 3 6 9
**>
**> , , 2
**>
**> [,1] [,2] [,3]
**> [1,] 12 15 18
**> [2,] 12 15 21
**> [3,] 12 18 21
**> [4,] 15 18 21
**>
**> Warning message:
**> STATS does not recycle exactly across MARGIN
**>
**> The code could be easily modified to warn in other cases, e.g. when
**> length of STATS is a divisor of the corresponding array extent (as in
**> the first example above, with length(STATS) = 2).
**>
**> The code also includes Gabor's suggestion.
**>
**> Heather
**>
**> sweep <- function (x, MARGIN, STATS, FUN = "-", warn =
**> getOption("warn"), ...)
**> {
**> FUN <- match.fun(FUN)
**> dims <- dim(x)
**> perm <- c(MARGIN, (1:length(dims))[-MARGIN])
**> if (warn >= 0) {
**> s <- length(STATS)
**> cumDim <- c(1, cumprod(dims[perm]))
**> if (s > max(cumDim))
**> warning("length of STATS greater than length of array",
**> call. = FALSE)
**> else {
**> upper <- min(ifelse(cumDim > s, cumDim, max(cumDim)))
**> lower <- max(ifelse(cumDim < s, cumDim, min(cumDim)))
**> if (any(upper %% s != 0, s %% lower != 0))
**> warning("STATS does not recycle exactly across MARGIN",
**> call. = FALSE)
**> }
**> }
**> FUN(x, aperm(array(STATS, dims[perm]), order(perm)), ...)
**> }
**>
**>>>> Gabor Grothendieck <ggrothendieck@gmail.com> 06/21/05 01:25pm >>>
**> \
**> Perhaps the signature should be:
**>
**> sweep(...other args go here..., warn=getOption("warn"))
**>
**> so that the name and value of the argument are consistent with
**> the R warn option.
**>
**> On 6/21/05, Robin Hankin <r.hankin@noc.soton.ac.uk> wrote:
**>>
**>> 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
**>>
**>> ______________________________________________
**>> R-help@stat.math.ethz.ch mailing list
**>> https://stat.ethz.ch/mailman/listinfo/r-help
**>> PLEASE do read the posting guide!
**>> http://www.R-project.org/posting-guide.html
**>>
**>
**>
*

-- Robin Hankin Uncertainty Analyst National Oceanography Centre, Southampton European Way, Southampton SO14 3ZH, UK tel 023-8059-7743 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.htmlReceived on Wed Jun 22 01:57:31 2005

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