Hello,
This has nothing to do with default arguments, wrappers, etc ... on the
R side.
The issue is the difference between :
> typeof( matrix((1:9), 3, 3) )
[1] "integer"
> typeof( matrix(seq(1,9)^2, ncol=3) )
[1] "double"
The constructor of NumericMatrix has no choice but to cast the input
matrix to a numeric matrix if it is passed an integer matrix, therefore
when "matrix" is an integer matrix, there are three R objects involved,
giving you what you call "correct output".
When you pass it a numeric matrix, no cast is required, so there is only
one R object, shared by matrix, orig and plus. which gives you what you
call "incorrect output".
Further comments:
- don't use Pairlist unless you understand what a pairlist is in R, e.g.
what the R functions pairlist, as.pairlist, etc ... do. If you really
want to return a list, then use List::create, something like:
using namespace Rcpp;
return List::create( _["original"] = orig, _["plus"] = plus ) ;
This way, you'll get a real list (i.e. what the R function "list"
produces) which is more likely to be what you want
- Rcpp objects (Rcpp::NumericMatrix) don't copy data if they don't need
to, they just alter the way the data is perceived, so that you can
manipulate the matrix using c++ syntax, operators, etc ... hence Dirk's
comments. If you really wanted two distinct objects, you can use the
clone function:
Rcpp::NumericMatrix orig( matrix ) ;
Rcpp::NumerixMatrix plus = Rcpp::clone( orig ) ;
This will give you the deep copy Dirk teased you with.
Romain
Le 25/05/10 03:58, Yi-Hsin Erica Tsai a écrit :
Hi,
I've just started using Rcpp with the hopes of speeding up some R loops
through replacement with C++ code. I've been struggling with
understanding the behavior of the NumericMatrix datatype and more
generally how to pass matrices between R and C++.
I seem to be getting bizarre behavior when I pass default parameters to
my C++ functions. For example, take this C++ function and the
corresponding R wrapper function:
______________________________________
//testRcppMatrix.cpp
#include <Rcpp.h>
RcppExport SEXP plusonediag_RcppMatrix(SEXP matrix)
{
Rcpp::NumericMatrix orig(matrix);
Rcpp::NumericMatrix plus(matrix);
int n = orig.rows();
int k = orig.cols();
for (int i=0; i<n; i++)
{
if(i <= k)
{
plus(i,i) = plus(i,i) + 1;
}
}
Rcpp::Pairlist res(Rcpp::Named( "original", orig),
Rcpp::Named( "plus", plus)
);
return res;
}
______________________________________
#testRcpp.r
plusonediag_RcppMatrix_wrapper <- function(mat=matrix(seq(1,9)^2, ncol=3))
{
## Make the call...
val <- .Call("plusonediag_RcppMatrix",
mat)
return(val)
}
______________________________________
If I pass actual values to the plusonediag_RcppMatrix_wrapper, then I
get correct output; however, if I try to use the default parameter (mat)
or pass a matrix equal to the default matrix, then the original matrix
appears to be overwritten. See the session output below.
Anyone have any idea what I'm doing wrong? I'd appreciate any help or
insight into this problem.
I've attached the test files if that's helpful.
Thanks and best wishes,
--Erica Tsai
> # main.r
>
> library(Rcpp)
Loading required package: inline
> dyn.load("testRcppMatrix.so")
> source("testRcppMatrix.r")
>
> foo <- matrix(1:9, 3, 3)
> bar <- foo ^ 2
>
> plusonediag_RcppMatrix_wrapper #default mat is same as bar
function(mat=matrix(seq(1,9)^2, ncol=3))
{
## Make the call...
val <- .Call("plusonediag_RcppMatrix",
mat)
return(val)
}
> plusonediag_RcppMatrix_wrapper() #does not produce correct output!!
$original
[,1] [,2] [,3]
[1,] 2 16 49
[2,] 4 26 64
[3,] 9 36 82
$plus
[,1] [,2] [,3]
[1,] 2 16 49
[2,] 4 26 64
[3,] 9 36 82
> plusonediag_RcppMatrix_wrapper(foo) #produces correct output
$original
[,1] [,2] [,3]
[1,] 1 4 7
[2,] 2 5 8
[3,] 3 6 9
$plus
[,1] [,2] [,3]
[1,] 2 4 7
[2,] 2 6 8
[3,] 3 6 10
> plusonediag_RcppMatrix_wrapper(bar) #does not produce correct output!!
$original
[,1] [,2] [,3]
[1,] 2 16 49
[2,] 4 26 64
[3,] 9 36 82
$plus
[,1] [,2] [,3]
[1,] 2 16 49
[2,] 4 26 64
[3,] 9 36 82
> plusonediag_RcppMatrix_wrapper(matrix((1:9), 3, 3)) #produces correct
output
$original
[,1] [,2] [,3]
[1,] 1 4 7
[2,] 2 5 8
[3,] 3 6 9
$plus
[,1] [,2] [,3]
[1,] 2 4 7
[2,] 2 6 8
[3,] 3 6 10
> plusonediag_RcppMatrix_wrapper(matrix((1:9)^2, 3, 3)) #does not
produce correct output!!
$original
[,1] [,2] [,3]
[1,] 2 16 49
[2,] 4 26 64
[3,] 9 36 82
$plus
[,1] [,2] [,3]
[1,] 2 16 49
[2,] 4 26 64
[3,] 9 36 82
>
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--
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30
http://romainfrancois.blog.free.fr
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