Hi Jonathan,
Jonathan Fintzi has written at Wed, 12 Oct 2016 13:43:20 -0700
Hello,
I am trying to use the std::copy() function to copy elements from an
Rcpp::NumericVector into rows of armadillo matrices. A simplified
version of my code is as follows:
cppFunction('void copyinto(Rcpp::NumericVector& v, arma::mat& d1,
arma::mat& d2) {
std::copy(v.begin(), v.begin() + 3, d1.begin_row(0));
std::copy(v.begin() + 3, v.end(), d2.begin_row(0));
}', depends = "RcppArmadillo")
v <- runif(6)
d1 <- matrix(0.0, 3,3)
d2 <- matrix(0.0, 3,3)
copyinto(v, d1, d2)
However, when I attempt to compile the code, I receive a list of
compilation errors including "no type named 'XXXXXX' in 'class
arma::Mat<double>row_iterator", where XXXXXX is iterator_category,
value_type, difference_type, pointer, and reference.
If I change the iterators to column iterators (e.g. d1.begin_col(0))
everything compiles and works just fine. I feel that I must be missing
something quite basic here, but in searching around I haven't been
able to identify my mistake.
May be the problem is that you are trying to use std::copy for writing
to non contiguous memory when you use a row pointer and the class writers
were smart enough to prevent such situation.
The following code works as expected, may be it can do the job for you:
cppFunction('void copy2(arma::rowvec& v, arma::mat& d1, arma::mat& d2) {
d1.row(0)=v(arma::span(0,2));
d2.row(0)=v(arma::span(3,5));
}', depends = "RcppArmadillo")
v <- runif(6)
d1 <- matrix(0.0, 3,3)
d2 <- matrix(0.0, 3,3)
copy2(v, d1, d2)
Thank you for your help!
Jon
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