[Rcpp-devel] How to figure out the signature of cxxfunction is a matrix or vector?

[Dirk Eddelbuettel]

On 21 August 2012 at 21:43, Peng Yu wrote:
| Hi,
| 
| "numeric" is specified as the signature. But it does not say whether

a) Not that even "numeric" is just a placeholder. You could replace it with
   "groucho_marx" and the code still runs.

   The only thing really used is the _left-hand side_ (here 'mx') which gets
   used for the variable name.

b) In R, vector and matrix are rather close -- almost the same. Matrices are
   vectors which happen to have a dimension attribute. We make that point in
   the documentation.

| it should be a matrix or a vector. The following example just assume
| the input is matrix. But should there be some checking to make sure
| the input is indeed a matrix before the conversion to NumericMatrix?

The test happens when the object is instantiated:

   R> library(inline)
   R> 
   R> src='
   +  Rcpp::NumericVector mat =
   +  Rcpp::clone<Rcpp::NumericMatrix>(mx);
   +  std::transform(mat.begin(), mat.end(), mat.begin(), ::sqrt);
   +  return mat;
   + '
   R> 
   R> fun <- cxxfunction(signature(mx="numeric"), src, plugin="Rcpp")
   R> 
   R> orig <- matrix(1:9, 3, 3)
   R> fun(orig)
           [,1]    [,2]    [,3]
   [1,] 1.00000 2.00000 2.64575
   [2,] 1.41421 2.23607 2.82843
   [3,] 1.73205 2.44949 3.00000
   R> 
   R> orig2 <- 1:9
   R> fun(orig2)
   Error in fun(orig2) : not a matrix
   R> 

which is not much different from passing in other inadmissible objects:

   R> fun(c("A","B"))
   Error in fun(c("A", "B")) : not a matrix
   R> fun(NULL)
   Error in fun(NULL) : not a matrix
   R> 

If you want a test at the cxxfunction level, you need to write a different
cxxfunction that implements tests. 

Dirk

| Or the check has to be before "fun" is called?
| 
| Thanks!
| 
| library(inline)
| src='
| Rcpp::NumericVector mat =
| Rcpp::clone<Rcpp::NumericMatrix>(mx);
| std::transform(mat.begin(), mat.end(),
|   mat.begin(), ::sqrt);
| return mat;
| '
| fun=cxxfunction(signature(mx="numeric"), src,
|   plugin="Rcpp")
| orig=matrix(1:9, 3, 3)
| fun(orig)
| 
| 
| -- 
| Regards,
| Peng
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-- 
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com