I have been asked (by Roger; thank you for the good question, and I hope it's fine to answer to the public) : > with Pi a sparse matrix and x,y, and ones > compatible n-vectors — when I do:
>> c(t(x) %*% Pi %*% ones, t(ones) %*% Pi %*% y ) > [[1]] 1 x 1 Matrix of class "dgeMatrix" > [,1] [1,] > 0.1338527 > [[2]] 1 x 1 Matrix of class "dgeMatrix" [,1] [1,] > 0.7810341 > I get a list whereas if Pi is an ordinary matrix I get a > vector. Is this intentional? Well, no. But it has been "unavoidable" in the sense that it had not been possible to provide S4 methods for '...' in the "remote" past, when Matrix was created. Later ... also quite a few years ago, John Chambers had added that possibility, with still some limitation (all '...' must be of the same class), and also plans to remove some of the limitations, see ?dotsMethods in R. I honestly have forgotten the history of my trying to provide 'c' methods for our "Matrix" objects after the 'dotsMethods' possibility had emerged, but I know I tried and had not seen a way to succeed "satisfactorily", but maybe I now think I maybe should try again. I currently think this needs changes to R before it can be done satisfactorily, and this is the main reason why this is a public answer to R-devel@..., but I'm happy if I'am wrong. The real challenge here is that I think that if it should "work", it should work so in all cases, e.g., also for c(NA, 3:2, Matrix(2:1), matrix(10:11)) and that's not so easy, e.g., the following class and method definitions do *not* achieve the desired result: ## "mMatrix" is already hidden in Matrix pkg: setClassUnion("mMatrix", members = c("matrix", "Matrix")) setClassUnion("numMatrixLike", members = c("logical", "integer","numeric", "mMatrix")) c.Matrix <- function(...) unlist(lapply(list(...), as.vector)) ## NB: Must use signature '(x, ..., recursive = FALSE)' : setMethod("c", "Matrix", function(x, ..., recursive) c.Matrix(x, ...)) ## The above is not sufficient for ## c(NA, 3:2, <Matrix>, <matrix>) : setMethod("c", "numMatrixLike", function(x, ..., recursive) c.Matrix(x, ...)) ## but the above does not really help: > c(Diagonal(3), NA, Matrix(10:11)) ## works fine, [1] 1 0 0 0 1 0 0 0 1 NA 10 11 > c(NA, Diagonal(3)) ## R's lowlevel c() already decided to use list(): [[1]] [1] NA [[2]] [,1] [,2] [,3] [1,] 1 . . [2,] . 1 . [3,] . . 1 > ---------------------------------------------- BTW, I (and the package users) suffer from exactly the same problem with the "MPFR" (multi precision numbers) provided by my package Rmpfr: > require(Rmpfr) > c(mpfr(3,100), 1/mpfr(7, 80)) ## works fine 2 'mpfr' numbers of precision 80 .. 100 bits [1] 3 0.14285714285714285714285708 > c(pi, 1/mpfr(7, 80)) ## "fails" even worse than in 'Matrix' case [[1]] [1] 3.141593 [[2]] 'mpfr1' 0.14285714285714285714285708 > Yes, it would be very nice if c(.) could be used to concatenate quite arbitrary R objects into one long atomic vector, but I don't see how to achieve this easily. The fact, that c() just builds a list of its arguments if it ("thinks" it) cannot dispatch to a method, is a good strategy, but I'd hope it should be possible to have c() try to do better (and hence work for this case, and without a noticable performance penalty. Suggestions are very welcome. Martin ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel