S+'s help(apply) says MARGIN the subscripts over which the function is to be applied. For example, if X is a matrix, MARGIN=1 indicates rows and MARGIN=2 indicates columns. If the dimensions of X are named, then the names can be used to specify MARGIN. Note that MARGIN tells which dimensions of X are retained in the result.
(and the Details section of the help file gives a worked example) but I don't know if that is any clearer to you than R's help(apply). So if you want to summarize the one-dimensional slices, X[i,j,k], of an I by J by K array X use MARGIN=c(1,2). (If your summary has dimensions M by N by ... by P (or just length M) then apply's output has dimensions c(prod(M,N,...,P),K), except that any dimension equal to 1 is dropped.) Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com From: Simone Salvadei [mailto:simone.salva...@gmail.com] Sent: Thursday, November 17, 2011 11:20 PM To: William Dunlap Subject: Re: [R] function sum for array thank you very much, despite of the fact that I didn't understand how it really works. Why have you put 1:2? S On Thu, Nov 17, 2011 at 9:40 PM, William Dunlap <wdun...@tibco.com> wrote: The following gives a result identical to your 'B'. > apply(A,1:2,sum) [,1] [,2] [,3] [1,] 532610 2130440 8521760 [2,] 1065220 4260880 17043520 Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On > Behalf Of Simone Salvadei > Sent: Thursday, November 17, 2011 8:25 AM > To: r-help@r-project.org > Subject: [R] function sum for array > > I'm looking for a function that allows to sum the elements of an array > along a dimension that can be different from the classical ones (rows or > columns). > > Let's suppose for example that: > > - A is an array with dimensions 2 x 3 x 4 > - I want to compute B, a 2 x 3 matrix with elements equal to the sum of the > corrensponding elements on each of the 3 strata. > > I've tried to use apply(A,3,sum) but the result is a vector, not a matrix. > Another solution is a less elegant > > B=matrix(rep(0,6),ncol=3) > for(t in 1:4) B = B + A[ , , t] > > May anybody help? > S > > -- > ------------------------------------------------------------------- > > Simone Salvadei > > Faculty of Economics > Department of Financial and Economic Studies and Quantitative Methods > University of Rome Tor Vergata > e-mail: simone.salva...@uniroma2.it <federico.belo...@uniroma2.it> > url: http://www.economia.uniroma2.it/phd/econometricsempiricaleconomics/ > <http://www.econometrics.it/> > ------------------------------------------------------------------- > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. -- ------------------------------------------------------------------- Simone Salvadei Faculty of Economics Department of Financial and Economic Studies and Quantitative Methods University of Rome Tor Vergata e-mail: simone.salva...@uniroma2.it url: http://www.economia.uniroma2.it/phd/econometricsempiricaleconomics/ ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
