Hi Martin, On 02/07/2012 08:32 AM, Martin Maechler wrote:
Martin Maechler<maech...@stat.math.ethz.ch> on Mon, 6 Feb 2012 15:35:36 +0100 writes:>> On Sat, Feb 4, 2012 at 10:38 AM, Martin Maechler >> <maech...@stat.math.ethz.ch> wrote: >> > The help has >> > >> >> Description: >> > >> >> 'nrow' and 'ncol' return the number of rows or columns present in 'x'. >> >> 'NCOL' and 'NROW' do the same treating a vector as 1-column matrix. >> > >> > and >> > >> >> x: a vector, array or data frame >> > >> > I'm proposing to extend these two convenience functions >> > to also work ``correctly'' for generalized versions of matrices. >> > >> > >> > The current implementation : >> > >> > NROW<- function(x) if(is.array(x)||is.data.frame(x)) nrow(x) else length(x) >> > NCOL<- function(x) if(is.array(x)&& length(dim(x))> 1L || is.data.frame(x)) ncol(x) else 1L >> > >> > only treats something as matrix when is.array(.) is true, >> > which is not the case, e.g., for multiprecision matrices from >> > package 'gmp' or for matrices from packages SparseM, Matrix or similar. >> > >> > Of course, all these packages could write methods for NROW, NCOL >> > for their specific matrix class, but given that the current >> > definition is so simple, >> > I'd find it an unnecessary complication. >> > >> > Rather I propose the following new version >> > >> > NROW<- function(x) if(length(dim(x)) || is.data.frame(x)) nrow(x) else length(x) >> > NCOL<- function(x) if(length(dim(x))> 1L || is.data.frame(x)) ncol(x) else 1L >> That makes me wonder about: >> DIM<- function(x) if (length(dim(x))> 1L) dim(x) else c(length(x), 1L) >> or maybe more efficiently: >> DIM<- function(x) { >> d<- dim(x) >> if (length(d)> 1L) dim(x) else c(length(x), 1L) >> } >> given that dim() is not always trivial to compute (e.g. for data >> frames it can be rather slow if you're doing it for hundreds of data >> frames) >> then NROW and NCOL could be exact equivalents to nrow and ncol. >> Hadley > Thank you, Hadley. > Indeed, your suggestion seems to make sense > {as far as it makes sense to have such simple functions to > exist in base at all, but as we already have NROW and NCOL ..} > So, I propose to adopt Hadley's DIM() proposal, modified to > DIM<- function(x) if(length(d<- dim(x))) d else c(length(x), 1L) > and wait a day or so (or longer for reasons of vacation!) before > committing it, so the public can raise opinions. Actually, the above --- building NROW() and NCOL() ond DIM() is not quite correct: NCOL<- function(x) DIM(x)[2L] will fail for x<- array(1:3, 3)
But that's because in your modified version of DIM() you changed Hadley's original proposed semantic. With the original semantic: DIM <- function(x) if(length(d <- dim(x)) >= 2L) d else c(length(x), 1L) things work as expected on array(1:3, 3): > x <- array(1:3, 3) > DIM(x) [1] 3 1 (Note that using >= 2L instead of > 1L is more readable as it emphasizes the fact that the returned vector will always have at least 2 elements.) Cheers, H.
so I think I'll stick for now with the generalizations to NROW() and NCOL(), using NROW<- function(x) if(length(d<- dim(x))) d[1L] else length(x) NCOL<- function(x) if(length(d<- dim(x))> 1L) d[2L] else 1L which incorporates Hadley's note that there are case where dim(.) is ``relatively expensive''. Note that the above are also (very slightly) more efficient than basing them on DIM(.). Martin ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
-- Hervé Pagès Program in Computational Biology Division of Public Health Sciences Fred Hutchinson Cancer Research Center 1100 Fairview Ave. N, M1-B514 P.O. Box 19024 Seattle, WA 98109-1024 E-mail: hpa...@fhcrc.org Phone: (206) 667-5791 Fax: (206) 667-1319 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
