the .col method gives you a subview_col :
arma_inline subview_col<eT> col(const uword col_num);
arma_inline const subview_col<eT> col(const uword col_num) const;
not an umat.
The name of the class implies that it is a "view" class, so a way to
look a data from another class. hence, no data of its own, so cheap copy.
double f3(arma::subview_col<unsigned int> Z) {
Z(1, 0) = 223;
return 99.9;
}
Also, including RcppArmadillo.h after Rcpp.h is wrong. You should only
include RcppArmadillo.h.
I should do something so that the compiler tells you this.
Romain
Le 10/12/12 16:49, Ramon Diaz-Uriarte a écrit :
Dear All,
I am trying to pass columns from an Armadillo matrix to a function, but
I'd like to pass just a reference to the column, not a copy of the column
and I do not seem to be able to do it "elegantly".
The code below (function f1) I think shows that passing X.col to a
function creates a copy (X.unsafe_col does too). We can pass &X as
argument, and the index of the column, as in f2. And that will not create
a copy. But I think this is not the right way of doing what I want to do
(to begin with, I'd rather not pass the column index to the function).
What am I getting wrong?
Best,
// [[Rcpp::depends(RcppArmadillo)]]
#include <Rcpp.h>
#include <RcppArmadillo.h>
using namespace Rcpp;
double f1(arma::umat Z) {
Z(0, 0) = 111;
Z(9, 0) = 111;
std::cout << "f1, this is Z " << std::endl << Z << std::endl;
return 33.3;
}
double f2(arma::umat &Z, const int c1) {
Z(1, 0) = 222;
return 66.6;
}
double f3(arma::umat &Z) {
Z(1, 0) = 223;
return 99.9;
}
// [[Rcpp::export]]
List f0(IntegerVector s1_, IntegerVector c1_){
const int s1 = as<int>(s1_);
const int c1 = as<int>(c1_);
arma::umat X(10, s1);
for(int j = 0; j < s1; ++j) {
for(int i = 0; i < 10; ++i) {
X(i, j) = i * 10 + j;
}
}
// in both cases, a copy seems to be made
//double fitness = f1(X.col(c1));
double outf1 = f1(X.unsafe_col(c1));
std::cout << "f0, this is X after f1" << std::endl << X << std::endl;
double outf2 = f2(X, c1);
std::cout << "f0, this is X after f2" << std::endl << X << std::endl;
// double outf3 = f3(X.unsafe_col(c1)); //will not work
//double outf3 = f3(X.col(c1)); //will not work
return List::create(Named("X") = wrap(X),
Named("of1") = outf1,
Named("of2") = outf2);
}
--
Romain Francois
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blog: http://romainfrancois.blog.free.fr
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