My error. Clearly I did not do enough testing. z <- array(1:24,dim=2:4) > all.equal(f(z,1),f2(z,1)) [1] TRUE > all.equal(f(z,2),f2(z,2)) [1] TRUE > all.equal(f(z,3),f2(z,3)) [1] "Attributes: < Component “dim”: Mean relative difference: 0.4444444 >" [2] "Mean relative difference: 0.6109091"
# Your earlier example > z <- array(1:120, dim=2:5) > all.equal(f(z,1),f2(z,1)) [1] TRUE > all.equal(f(z,2),f2(z,2)) [1] TRUE > all.equal(f(z,3),f2(z,3)) [1] "Attributes: < Component “dim”: Mean relative difference: 0.4444444 >" [2] "Mean relative difference: 0.1262209" > all.equal(f(z,4),f2(z,4)) [1] "Attributes: < Component “dim”: Mean relative difference: 0.5714286 >" [2] "Mean relative difference: 0.5855162" David C -----Original Message----- From: Bert Gunter [mailto:bgunter.4...@gmail.com] Sent: Thursday, June 1, 2017 2:00 PM To: David L Carlson <dcarl...@tamu.edu> Cc: Roy Mendelssohn - NOAA Federal <roy.mendelss...@noaa.gov>; R-help <r-help@r-project.org> Subject: Re: [R] Reversing one dimension of an array, in a generalized case ?? > z <- array(1:24,dim=2:4) > all.equal(f(z,3),f2(z,3)) [1] "Attributes: < Component “dim”: Mean relative difference: 0.4444444 >" [2] "Mean relative difference: 0.6109091" In fact, > dim(f(z,3)) [1] 2 3 4 > dim(f2(z,3)) [1] 3 4 2 Have I made some sort of stupid error here? Or have I misunderstood what was wanted? Cheers, Bert Bert Gunter "The trouble with having an open mind is that people keep coming along and sticking things into it." -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip ) On Thu, Jun 1, 2017 at 11:34 AM, David L Carlson <dcarl...@tamu.edu> wrote: > Here is an alternative approach using apply(). Note that with apply() you are > reversing rows or columns not indices of rows or columns so apply(junk, 2, > rev) reverses the values in each column not the column indices. We actually > need to use rev() on everything but the index we are interested in reversing: > > f2 <- function(a, wh) { > dims <- seq_len(length(dim(a))) > dims <- setdiff(dims, wh) > apply(apply(a, dims, rev), dims, t) > } > > # Your example > j1 <- junk[ , rev(1:10), ] > j2 <- f2(junk, 2) > all.equal(j1, j2) > # [1] TRUE > > # Bert's example > z1 <- f(z, 2) > z2 <- f2(z, 2) > all.equal(z1, z2) > # [1] TRUE > > ------------------------------------- > David L Carlson > Department of Anthropology > Texas A&M University > College Station, TX 77840-4352 > > > > > > > -----Original Message----- > From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of Bert Gunter > Sent: Thursday, June 1, 2017 12:46 PM > To: Roy Mendelssohn - NOAA Federal <roy.mendelss...@noaa.gov> > Cc: R-help <r-help@r-project.org> > Subject: Re: [R] Reversing one dimension of an array, in a generalized case > > How about this: > > f <- function(a,wh){ ## a is the array; wh is the index to be reversed > l<- lapply(dim(a),seq_len) > l[[wh]]<- rev(l[[wh]]) > do.call(`[`,c(list(a),l)) > } > > ## test > z <- array(1:120,dim=2:5) > > ## I omit the printouts > > f(z,2) > > f(z,3) > > > Cheers, > Bert > > Bert Gunter > > "The trouble with having an open mind is that people keep coming along > and sticking things into it." > -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip ) > > > On Thu, Jun 1, 2017 at 9:51 AM, Roy Mendelssohn - NOAA Federal > <roy.mendelss...@noaa.gov> wrote: >> Hi All: >> >> I have been looking for an elegant way to do the following, but haven't >> found it, I have never had a good understanding of any of the "apply" >> functions. >> >> A simplified idea is I have an array, say: >> >> junk(5, 10, 3) >> >> where (5, 10, 3) give the dimension sizes, and I want to reverse the second >> dimension, so I could do: >> >> junk1 <- junk[, rev(seq_len(10), ] >> >> but what I am after is a general function that will do that where the array >> could be two, three or four dimensions, and I pass to the function which >> dimension I want to reverse, that is the function can not assume the number >> of dimensions of the array nor which dimension to reverse. >> >> For example, if i try: >> >> junk1 <- apply(junk, 2, rev) >> >> junk1 comes out as two-dimensional, not three-dimensional. >> >> It is probably something obvious but I am not getting it. >> >> Thanks for any help. >> >> -Roy >> >> >> ********************** >> "The contents of this message do not reflect any position of the U.S. >> Government or NOAA." >> ********************** >> Roy Mendelssohn >> Supervisory Operations Research Analyst >> NOAA/NMFS >> Environmental Research Division >> Southwest Fisheries Science Center >> ***Note new street address*** >> 110 McAllister Way >> Santa Cruz, CA 95060 >> Phone: (831)-420-3666 >> Fax: (831) 420-3980 >> e-mail: roy.mendelss...@noaa.gov www: http://www.pfeg.noaa.gov/ >> >> "Old age and treachery will overcome youth and skill." >> "From those who have been given much, much will be expected" >> "the arc of the moral universe is long, but it bends toward justice" -MLK Jr. >> >> ______________________________________________ >> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see >> 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. > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
