[Rcpp-devel] accessing list elements without using names

[Sameer Soi]

I am not exactly sure why that works, but it does! Why doesn't it directly
see the NumericMatrix(SEXP)?

Thank you, Dirk!

On Fri, Feb 10, 2012 at 3:10 PM, Dirk Eddelbuettel <edd at debian.org> wrote:

>
> On 10 February 2012 at 14:49, Sameer Soi wrote:
> | Hello Rcpp'ers,
> |
> | I want to access a List of matrices in an Rcpp/C++ function that will
> passed to
> | me via R...
> |
> | src <- "
> |   using namespace Rcpp ;
> |   List inputList(L) ;
> |   NumericMatrix tmpMatrix ;
> |
> |   tmpMatrix = NumericMatrix(inputList[0]) ;
> |   return(wrap(tmpMatrix.ncol())) ;
> | "
> | test <- cxxfunction(signature(L="list"), src, plugin = "Rcpp" )
> |
> | This gives me the following error-
> |
> | file30b9664194fc.cpp: In function ‘SEXPREC* file30b9664194fc(SEXPREC*)’:
> | file30b9664194fc.cpp:34: error: call of overloaded ‘Matrix
> | (Rcpp::internal::generic_proxy<19>)’ is ambiguous
> | /usr/share/R/include/Rcpp/vector/SubMatrix.h:57: note: candidates are:
> | Rcpp::Matrix<RTYPE>::Matrix(const Rcpp::SubMatrix<RTYPE>&) [with int
> RTYPE =
> | 14]
> | /usr/share/R/include/Rcpp/vector/Matrix.h:67:
> | note:                 Rcpp::Matrix<RTYPE>::Matrix(const
> | Rcpp::Matrix<RTYPE>&) [with int RTYPE = 14]
> | /usr/share/R/include/Rcpp/vector/Matrix.h:65:
> | note:                 Rcpp::Matrix<RTYPE>::Matrix(const int&)
> | [with int RTYPE = 14]
> | /usr/share/R/include/Rcpp/vector/Matrix.h:46:
> | note:                 Rcpp::Matrix<RTYPE>::Matrix(const
> | Rcpp::Dimension&) [with int RTYPE = 14]
> | /usr/share/R/include/Rcpp/vector/Matrix.h:39:
> | note:                 Rcpp::Matrix<RTYPE>::Matrix(SEXPREC*)
> | [with int RTYPE = 14]
> | make: *** [file30b9664194fc.o] Error 1
> |
> | In looking at the error, it's not clear to me how these candidates will
> help.
> | What am I missing in telling Rcpp what class of object it should be
> expecting
> | coming out of inputList?
>
> Template code gets complicate. The subsetting (of the List) confuses here.
> And one more statement and all is well -- you were very close!
>
> R> library(inline)
> R> src <- '
> +   Rcpp::List inputList(L) ;
> +   Rcpp::NumericMatrix tmpMatrix ;
> +   SEXP tmp = inputList[0];
> +   tmpMatrix = Rcpp::NumericMatrix(tmp) ;
> +   return(wrap(tmpMatrix.ncol())) ;
> + '
> R> f <- cxxfunction(signature(L="list"), src, plugin = "Rcpp" )
> R> f(list(matrix(1:9,3,3)))
> [1] 3
> R>
>
>
> Hope this helps,  Dirk
>
> |
> | I know this kind of question (i.e. I want a 3d cube etc) pops up
> frequently and
> | the answer is typically "use arma's 3d cubes" (e.g.
> http://stackoverflow.com/
> | questions/8159872/r-list-of-numeric-vectors-c-2d-array-with-rcpp), but I
> don't
> | intend on doing linear algebra. My data really is just a series of
> matrices of
> | arbitrary sizes.
> |
> | Also, I looked into multi-dimensional arrays, but how to access them
> seems
> | unclear; I did see a post on this list to that nature but the solution
> seemed
> | inelegant.
> |
> | Thanks in advance for any help!
> |
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> "Outside of a dog, a book is a man's best friend. Inside of a dog, it is
> too
> dark to read." -- Groucho Marx
>



-- 
Sameer Soi

w: 215.746.2683 | c: 814.241.8585
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