[Rcpp-devel] Deep copying a matrix

[Etienne B. Racine]

Hi list,

I'm struggling with the copy of my parameters. If I understand correctly, if
you ship an int matrix to the function, you'll get a deep copy. However if
it's a numeric matrix, then there's no copy and you get a matrix pointing on
your R matrix. That's funny when you try to debug as one might work and the
other not.

Here's an illustration
library(Rcpp); library(inline)

f1 <- cxxfunction(signature(origin="numeric"), body = "
                  Rcpp::NumericMatrix m_source(origin);
                  m_source(0,0) = 0;
                  cout << origin << endl << m_source << endl ; ",
                  include = "using namespace std;",
                  plugin="Rcpp")

m <- matrix(1:4,2,2)
x <- f1(m)

#0x9c7fe18
#0xb416a1a8  # differentm#     [,1] [,2]
#[1,]    1    3
#[2,]    2    4m <- matrix(1:4/2,2,2)x <- f1(m)#0xb416a090
#0xb416a090  # no differentm#     [,1] [,2]
#[1,]    0  1.5
#[2,]    1  2.0


Now, what I'd like is to have a (deep) copy of that matrix, whatever the
type. I've tried
Rcpp::NumericMatrix m_copy = m_source; // of course it did not work, but
never know with vectorisation ;-)
sdt::copy(m_source.begin(), m_source.end(), std::back_inserter(m_copy)) //
nope

The closer I got was with
f2 <- cxxfunction(signature(origin="numeric"), body = "
                  Rcpp::NumericMatrix m_source(origin);
                  Rcpp::NumericMatrix m_copy;
                  Rcpp::NumericMatrix::iterator itr;
                  cout << m_copy << endl << endl;
                  m_source(0,0) = 0;
                  for(itr = m_source.begin(); itr != m_source.end(); ++itr)
                    m_copy.push_back(*itr);
                  m_copy[3] = 1; // matrix structure is lost or never
existed;
                  cout << origin << endl << m_source << endl << m_copy ;
                  return wrap(m_copy);",
                  include = "using namespace std;",
                  plugin="Rcpp", verbose= FALSE)

Main drawback is that I loose the matrix structure. I'm sure there's a
correct way to do this, but I couldn't find it.

Etienne
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