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[Rcpp-devel] Working with arma::cube

4 messages · Silkworth,David J., Dirk Eddelbuettel, Alexios Ghalanos

Original
Silkworth,David J.
# 
I am helping a student build some R code in Rcpp for his first time.  He is working with 3-dimensional arrays, so I am hopeful to be working with arma::cube objects.

When I simply try to bring the array in as an argument I can't seem to use the same as<[TEMPLATE]> construction as other objects.

arma::cube X=Rcpp::as<arma::cube>(arg1);

This line fails to compile.

I can build this cube from an input vector using explicit nested loops.  I also notice that wrap() does a fine job of returning the array back to R.

Is there anything else I need to know to more simply bring the array in as an SEXP and land it in the arma::cube.

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Dirk Eddelbuettel
#
On 6 March 2013 at 00:50, Silkworth,David J. wrote:
| I am helping a student build some R code in Rcpp for his first time.  He is
| working with 3-dimensional arrays, so I am hopeful to be working with
| arma::cube objects.
|  
| When I simply try to bring the array in as an argument I can?t seem to use the
| same as<[TEMPLATE]> construction as other objects.
|  
| arma::cube X=Rcpp::as<arma::cube>(arg1);
|  
| This line fails to compile.

Yes. Nobody wrote such a converter. Maybe you and your student want to take a stab?
  
| I can build this cube from an input vector using explicit nested loops.  I also
| notice that wrap() does a fine job of returning the array back to R.
|  
| Is there anything else I need to know to more simply bring the array in as an
| SEXP and land it in the arma::cube.

Array plus dim attribute may work.  

I used arma::cube quite extensively in one project, but only at the C++ level
as a container. Results back to R were always of lesser dimension.

Dirk
Alexios Ghalanos
# 
Try this:

library(RcppArmadillo)
library(inline)
if( require( RcppArmadillo ) ){
	fx <- cxxfunction( signature(x = "vector", n = "integer") , '
		Rcpp::NumericVector XX(x);
		Rcpp::IntegerVector dim(n);
		arma::cube AY(XX.begin(), dim[0], dim[1], dim[2]);
		return(wrap(AY));
	', plugin = "RcppArmadillo" )
}

set.seed(10)
x = array(rnorm(25*25*10), dim=c(25,25,10))
y = fx(x, c(25,25,10))
all.equal(x,y)

Regards,
Alexios
On 06/03/2013 01:15, Dirk Eddelbuettel wrote:
Dirk Eddelbuettel
#
On 6 March 2013 at 03:22, alexios ghalanos wrote:
| Try this:
| 
| library(RcppArmadillo)
| library(inline)
| if( require( RcppArmadillo ) ){
| 	fx <- cxxfunction( signature(x = "vector", n = "integer") , '
| 		Rcpp::NumericVector XX(x);
| 		Rcpp::IntegerVector dim(n);
| 		arma::cube AY(XX.begin(), dim[0], dim[1], dim[2]);
| 		return(wrap(AY));
| 	', plugin = "RcppArmadillo" )
| }
| 
| set.seed(10)
| x = array(rnorm(25*25*10), dim=c(25,25,10))
| y = fx(x, c(25,25,10))
| all.equal(x,y)

Very nice. 

And it provides a blueprint for an as<>() converter, especially as the dim
vector could be picked off as attribute rather than a second argument.

Dirk
 
| Regards,
| Alexios
|
| On 06/03/2013 01:15, Dirk Eddelbuettel wrote:
| >
| > On 6 March 2013 at 00:50, Silkworth,David J. wrote:
| > | I am helping a student build some R code in Rcpp for his first time.  He is
| > | working with 3-dimensional arrays, so I am hopeful to be working with
| > | arma::cube objects.
| > |
| > | When I simply try to bring the array in as an argument I can?t seem to use the
| > | same as<[TEMPLATE]> construction as other objects.
| > |
| > | arma::cube X=Rcpp::as<arma::cube>(arg1);
| > |
| > | This line fails to compile.
| >
| > Yes. Nobody wrote such a converter. Maybe you and your student want to take a stab?
| >
| > | I can build this cube from an input vector using explicit nested loops.  I also
| > | notice that wrap() does a fine job of returning the array back to R.
| > |
| > | Is there anything else I need to know to more simply bring the array in as an
| > | SEXP and land it in the arma::cube.
| >
| > Array plus dim attribute may work.
| >
| > I used arma::cube quite extensively in one project, but only at the C++ level
| > as a container. Results back to R were always of lesser dimension.
| >
| > Dirk
| >
| 
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