Reversing one dimension of an array, in a generalized case
On Jun 1, 2017, at 9:51 AM, Roy Mendelssohn - NOAA Federal <roy.mendelssohn at 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.
It was clear whether you wanted every slice along a particular dimension reversed or just one particular slice in a particular dimension. I thought probably the former: Try: (arr <- array(1:(2*3*4), dim=c(2,3,4) ) ) array( apply(arr, 3, rev), dim (arr) )
David. > > 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.Mendelssohn at 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 at 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. David Winsemius Alameda, CA, USA