[Rcpp-devel] RcppEigen: Getting and setting dimnames of sparse matrix

[Douglas Bates]

The Eigen sparse matrix only contains the numeric information, it doesn't
contain information like Dimnames that are specific to the R structure.  If
you want to access the slots or set their values it is easiest to do that
with the Rcpp::S4 class object.

Of course it helps to use R's str function first to ensure that you know
what the structure actually is.
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> library(Matrix)
Loading required package: lattice
> library(RcppEigen)
Loading required package: Rcpp
> library(inline)
> 
> ugM     <- new("dgCMatrix"
+                , i = c(1L, 0L, 2L, 1L)
+                , p = c(0L, 1L, 3L, 4L)
+                , Dim = c(3L, 3L)
+                , Dimnames = list(c("a", "b", "c"), c("a", "b", "c"))
+                , x = c(1, 1, 1, 1)
+                , factors = list())
> ugM
3 x 3 sparse Matrix of class "dgCMatrix"
  a b c
a . 1 .
b 1 . 1
c . 1 .
> str(ugM)
Formal class 'dgCMatrix' [package "Matrix"] with 6 slots
  ..@ i       : int [1:4] 1 0 2 1
  ..@ p       : int [1:4] 0 1 3 4
  ..@ Dim     : int [1:2] 3 3
  ..@ Dimnames:List of 2
  .. ..$ : chr [1:3] "a" "b" "c"
  .. ..$ : chr [1:3] "a" "b" "c"
  ..@ x       : num [1:4] 1 1 1 1
  ..@ factors : list()
> 
> src <- '
+ typedef Eigen::SparseMatrix<double> SpMat;
+ S4    Xin(XX_);
+ SpMat X(as<SpMat>(XX_));
+ S4    Xout(wrap(X));
+ Xout.slot("Dimnames") = Xin.slot("Dimnames");
+ return(Xout);
+ '
> 
> names_ <- cxxfunction(signature(XX_="dsCMatrix"), plugin="RcppEigen",
+         body=src)
> 
> names_(ugM)
3 x 3 sparse Matrix of class "dgCMatrix"
  a b c
a . 1 .
b 1 . 1
c . 1 .
> 
> 
> proc.time()
   user  system elapsed 
 10.356   0.436  10.859