[Rcpp-devel] Sparse matrices with RcppArmadillo

[Romain Francois]

That looks very similar, if not identical to what dgCMatrix uses. Can 
you direct me to a constructor where I could feed such information ?

Romain

Le 08/12/12 17:35, c s a écrit :
> Armadillo sparse matrices are stored in Compressed Sparse Column format:
>
> http://en.wikipedia.org/wiki/Sparse_matrix#Compressed_sparse_column_.28CSC_or_CCS.29
>
> This layout is used by a majority of external solvers.
>
> It would be far more efficient to take this layout into account when
> copying matrices, instead of blindly (and slowly) copying element by
> element.
>
>
> On Sunday, December 9, 2012, Romain Francois <romain at r-enthusiasts.com
> <mailto:romain at r-enthusiasts.com>> wrote:
>  > Le 08/12/12 09:45, Søren Højsgaard a écrit :
>  >>
>  >> Dear all,
>  >>
>  >> I want to use a matrix (of type "dgCMatrix" from the Matrix package)
> in RcppArmadillo, so I do:
>  >>
>  >> library(inline)
>  >> src <- '
>  >> using namespace arma;
>  >> using namespace Rcpp;
>  >> SpMat<double> X = as<SpMat<double> >(XX_);
>  >> '
>  >> foo <- cxxfunction(signature(XX_=""), body=src, plugin="RcppArmadillo")
>  >>
>  >> - but this fails. It seems to me (browsing the web) that SpMat are
> supported, but I might be wrong here. I have no indication that
> dgCMatrix matrices can be "converted" to SpMat's. I know that I can work
> with dgCMatrix matrices with RcppEigen, but what I need is to extract
> submatrices and that is very easy to do with RcppArmadillo.
>  >>
>  >> Any thoughts? Thanks in advance.
>  >> Regards
>  >> Søren
>  >
>  > Doug might know better about the internals of Matrix types. This is
> just following the recipee from how these are handled in RcppEigen:
>  >
>  > #include <RcppArmadillo.h>
>  > // [[Rcpp::depends(RcppArmadillo)]]
>  > using namespace Rcpp ;
>  >
>  > // [[Rcpp::export]]
>  > void convert(S4 mat){
>  >     IntegerVector dims = mat.slot( "Dim" ) ;
>  >     IntegerVector i = mat.slot( "i" ) ;
>  >     IntegerVector p = mat.slot( "p" ) ;
>  >     NumericVector x = mat.slot( "x" ) ;
>  >
>  >     int nrow = dims[0], ncol = dims[1] ;
>  >     arma::sp_mat res( nrow, ncol) ;
>  >     for(int j = 0; j < ncol; ++j) {
>  >         for (int k = p[j]; k < p[j + 1]; ++k) res( i[k], j ) = x[k];
>  >     }
>  >     std::cout << res << std::endl ;
>  >
>  > }
>  >
>  >
>  > /*** R
>  >     require(Matrix)
>  >     i <- c(1,3:8); j <- c(2,9,6:10); x <- 7 * (1:7)
>  >     ( A <- sparseMatrix(i, j, x = x) )
>  >
>  >     convert(A)
>  > ***/
>  >
>  > I don't think there is a better way to fill multiple values ina
> SpMat, maybe Conrad has insights.
>  >
>  > Romain
>  >
>  > --
>  > Romain Francois
>  > Professional R Enthusiast
>  > +33(0) 6 28 91 30 30
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-- 
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30

R Graph Gallery: http://gallery.r-enthusiasts.com

blog:            http://romainfrancois.blog.free.fr
|- http://bit.ly/RE6sYH : OOP with Rcpp modules
`- http://bit.ly/Thw7IK : Rcpp modules more flexible