[Rcpp-devel] appearance of matrix returned from Rcpp

[Jack Wasey]

Hello,

I am trying to return a matrix derived from a std::vector<bool> with row
names.

I followed the advice of Kevin and Dirk I read at
https://stackoverflow.com/questions/19864226/convert-stdvector-to-rcpp-matrix

Strangely, the matrix is correct, but when I print it in R, it prints
differently to defining it in R:

#include <Rcpp.h>
#include <string>
// [[Rcpp::export]]
SEXP make_mat(std::vector<bool> x, std::vector<std::string> n, int nrow,
int ncol) {
Rcpp::LogicalVector y = Rcpp::wrap(x);
y.attr("dim") = Rcpp::Dimension(nrow, ncol);
y.attr(".Dimnames") = Rcpp::List::create(n, R_NilValue);
return y;
}

rcpp_mat <- make_mat(c(T,T,F,F), c("a", "b"), 2, 2)
rcpp_mat
     [,1]  [,2]
[1,] TRUE FALSE
[2,] TRUE FALSE
attr(,".Dimnames")
attr(,".Dimnames")[[1]]
[1] "a" "b"

attr(,".Dimnames")[[2]]
NULL

rmat
  [,1]  [,2]
a TRUE FALSE
b TRUE FALSE

> typeof(rmat)
[1] "logical"
> typeof(rcpp_mat)
[1] "logical"
> class(rmat)
[1] "matrix"
> class(rcpp_mat)
[1] "matrix"

identical(rmat, rcpp_mat)
[1] FALSE

What's going on here, please?

Ideally, I'd rather construct a LogicalMatrix directly from
std::vector<bool>, but I don't think you have that constructor.

Thanks, Jack.