Using the Matrix package, how can I create a row-oriented sparse Matrix from scratch populated with some data? By default a column-oriented one is created and I'm aware of the note that the package is optimized for column-oriented ones, but I'm only interested in using it for holding my sparse row-oriented data and doing basic subsetting by rows (even using drop=FALSE).
Here is what I get when I set up a column-oriented sparse Matrix: > Cc <- Matrix(0, nrow=5, ncol=5, sparse=TRUE) > Cc[1:3,1] <- 1 > Cc 5 x 5 sparse Matrix of class "dgCMatrix" [1,] 1 . . . . [2,] 1 . . . . [3,] 1 . . . . [4,] . . . . . [5,] . . . . . > str(Cc) Formal class 'dgCMatrix' [package "Matrix"] with 6 slots ..@ i : int [1:3] 0 1 2 ..@ p : int [1:6] 0 3 3 3 3 3 ..@ Dim : int [1:2] 5 5 ..@ Dimnames:List of 2 .. ..$ : NULL .. ..$ : NULL ..@ x : num [1:3] 1 1 1 ..@ factors : list() When I try to do the analogue for a row-oriented matrix, I get a "dgTMatrix", whereas I would expect a "dgRMatrix": > Cr <- Matrix(0, nrow=5, ncol=5, sparse=TRUE) > Cr <- as(Cr, "dsRMatrix") > Cr[1,1:3] <- 1 > Cr 5 x 5 sparse Matrix of class "dgTMatrix" [1,] 1 1 1 . . [2,] . . . . . [3,] . . . . . [4,] . . . . . [5,] . . . . . > str(Cr) Formal class 'dgTMatrix' [package "Matrix"] with 6 slots ..@ i : int [1:3] 0 0 0 ..@ j : int [1:3] 0 1 2 ..@ Dim : int [1:2] 5 5 ..@ Dimnames:List of 2 .. ..$ : NULL .. ..$ : NULL ..@ x : num [1:3] 1 1 1 ..@ factors : list() Trying with explicit coercion does not work: > as(Cc, "dgRMatrix") Error in as(Cc, "dgRMatrix") : no method or default for coercing "dgCMatrix" to "dgRMatrix" > as(Cr, "dgRMatrix") Error in as(Cr, "dgRMatrix") : no method or default for coercing "dgTMatrix" to "dgRMatrix" Am I doing some wrong here? Or is this what means that the package is optimized for the column-oriented representation and I shouldn't really work with row-oriented ones? I'm really only interested in access to efficient Cr[row,,drop=FALSE] subsetting (and a small memory footprint). Thanks, Henrik ______________________________________________ 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.
