[Rcpp-devel] Problems indexing matrics

[Yasir Suhail]

From
http://dirk.eddelbuettel.com/code/rcpp/html/Matrix_8h_source.html#l00058
The constructor for matrix is Matrix(nrow, ncol, iterator), there is no
constructor it seems for initializing the default value. So your problem is
Rcpp::NumericMatrix output(x_s + x_k - 1, y_s + y_k - 1, 0.0);
should be
Rcpp::NumericMatrix output(x_s + x_k - 1, y_s + y_k - 1);

and then a separate loop for initialization. I'd like to know if someone
knows of another way of initialization.

yasir

On Wed, Jan 4, 2012 at 3:13 PM, Hadley Wickham <hadley at rice.edu> wrote:

> Hi all,
>
> As I'm (slowly) getting more proficient with Rcpp, I'm attempting to
> write a 2d convolution function. My latest attempt:
>
> convolve2d <- cxxfunction(signature(sampleS = "numeric", kernelS =
> "numeric"), plugin = "Rcpp", '
>    Rcpp::NumericMatrix sample(sampleS), kernel(kernelS);
>    int x_s = sample.nrow(), x_k = kernel.nrow();
>    int y_s = sample.ncol(), y_k = kernel.ncol();
>
>    Rcpp::NumericMatrix output(x_s + x_k - 1, y_s + y_k - 1, 0.0);
>    for (int row = 0; row < x_s; row++) {
>      for (int col = 0; col < y_s; col++) {
>        for (int i = 0; i < x_k; i++) {
>          for (int j = 0; j < y_k; j++) {
>            output(row, col) += sample(row + i, col + j) * kernel(i, j);
>          }
>        }
>      }
>    }
>    return output;
> ')
>
> fails to compile with a not very informative error message:
>
> Error in compileCode(f, code, language = language, verbose = verbose) :
>  Compilation ERROR, function(s)/method(s) not created!
> /usr/include/c++/4.2.1/bits/stl_iterator_base_types.h: In
> instantiation of ‘std::iterator_traits<double>’:
> /Users/hadley/R/Rcpp/include/Rcpp/internal/wrap.h:346:   instantiated
> from ‘SEXPREC* Rcpp::internal::range_wrap(InputIterator,
> InputIterator) [with InputIterator = double]’
> /Users/hadley/R/Rcpp/include/Rcpp/internal/wrap.h:847:   instantiated
> from ‘SEXPREC* Rcpp::wrap(InputIterator, InputIterator) [with
> InputIterator = double]’
> /Users/hadley/R/Rcpp/include/Rcpp/vector/Vector.h:418:   instantiated
> from ‘void Rcpp::Vector<RTYPE>::assign(InputIterator, InputIterator)
> [with InputIterator = double, int RTYPE = 14]’
> /Users/hadley/R/Rcpp/include/Rcpp/vector/Vector.h:249:   instantiated
> from ‘Rcpp::Vector<RTYPE>::Vector(InputIterator, InputIterator) [with
> InputIterator = double, int RTYPE = 14]’
> /Users/hadley/R/Rcpp/include/Rcpp/vector/Matrix.h:60:   instantiated
> from ‘Rcpp::Matrix<RTYPE>::Matrix(const i
>
> How can I use that error message to figure out what I'm doing wrong?
>
> I'm also wondering if since I'm using () to index, should I be using 1
> based indices?  I think that's the difference for () and [] for
> vectors, but I might just be confused.
>
> (Of course a separate question is whether this code actually
> implements 2d convolution or not, but it should hopefully be close)
>
> Hadley
>
>
> --
> Assistant Professor / Dobelman Family Junior Chair
> Department of Statistics / Rice University
> http://had.co.nz/
> _______________________________________________
> Rcpp-devel mailing list
> Rcpp-devel at lists.r-forge.r-project.org
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>
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