[Rcpp-devel] NumericVector

[James Li]

Hi Dirk,

N could be anywhere between 3-10.

Thanks! I will definitely look into how to do those.

Also, if

Rcpp::NumericVector vec3 =Rcpp::NumericVector( Rcpp::Dimension(4, 5, 6));

In this case, how do we access element vec3[1,2,3]?

Thanks again,
James

On Friday, August 16, 2013, Dirk Eddelbuettel wrote:

>
> Hi James,
>
> On 16 August 2013 at 11:59, James Li wrote:
> | Dear Dirk and Rcpp-devel members,
> |
> | I am currently passing a multidimensional (N > 2) array (i.e.
> | array(NA, dim = rep(3,5)) ) from R via Rcpp using
>
>
> How big is 'N' going to be?
>
> | "in C++:"
> |
> | //[[Rcpp::export]]
> | Rcpp::List check_arrayC (Rcpp::NumericVector x, Rcpp::IntegerVector
> modes){
> | //do stuff to x
> |     return Rcpp::List::create(Rcpp::_["data"] = x, Rcpp::_["modes"] =
> modes);
> | }
> |
> |
> | "in R:"
> |
> | a <- array(1:32, dim=rep(2,5))
> | b <- check_arrayC(a, dim(a))
> |
> | While I know that a multidimensional array is stored as a contiguous
> | array internally, is there currently a more natural/efficient way to
> | pass it back and forth within Rcpp?
> |
> | Also from Dirk's book, it seems that an instance of
> | Rcpp::NumericVector can be instantiated into a multidimensional array
> | via
> |
> | Rcpp::NumericVector vec3 =Rcpp::NumericVector( Rcpp::Dimension(4, 5, 6));
> |
> | In this case, how do we access element vec3[1,2,3]?
> |
> | Some background about what I am trying to do: I would like to create a
> | multidimensional array wrapper class around the base R multi-way array
> | class. I would also like to be able to pass this multidimensional
> | array via Rcpp to do all the heavy-lifting in c++. Ideally, I could
> | also convert the mda into a Boost::multi_array.
>
> For a moderately-sized project (at work, not open source) I had a very good
> experience using Armadillo 'cubes' (3-d matrices) which I occassionally
> stored in 'fields' (which I though of as lists of such cubes).  I think in
> most (all?) cases I reduces data to 2-d matrices before returning that
> R. That worked great.
>
> Beyond that ... you are on your own as there is very little C++ support
> already useable by Rcpp.  You'd have to write custom as<>() and wrap()
> methods (which is not hard and may well be worth it).
>
> Cheers, Dirk
>
> | Thanks in advance for any help.
> |
> | -James
> |
> | --
> | James Li | Ph.D. Candidate | http://jamesyili.com/
> | Dept. of Statistical Science | Cornell University
> | _______________________________________________
> | Rcpp-devel mailing list
> | Rcpp-devel at lists.r-forge.r-project.org <javascript:;>
> | https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
>
> --
> Dirk Eddelbuettel | edd at debian.org <javascript:;> |
> http://dirk.eddelbuettel.com
>


-- 
James Li *|* Ph.D. Candidate *|* http://jamesyili.com/
Dept. of Statistical Science *|* Cornell University
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