Passing attributes to Rcpp::Function

Question

I'm trying to pass a vector to the R function called from within Rcpp:

Rcpp::Function aperm("aperm");
int perm[3] = {2,1,3};
arr = aperm(arr, Rcpp::Named("perm", perm));

I've tried to wrap the perm before calling aperm but in both cases I am getting various Rcpp errors:

arr = aperm(arr, Rcpp::Named("perm", Rcpp::wrap(perm)));

Is it possible to pass a vector as a parameter to an R function when calling it from Rcpp?

score 4 · Accepted Answer · answered Oct 12 '12 at 11:17

4

Yes, it is but you need to make sure you use Rcpp::wrap() -- maybe explicitly if the implicit templated form is not called for you. Here, your C function array perm is of the wrong form. Make that an IntegerVector and things should work.

In general, complete and reproducible examples posted to the rcpp-devel list are the best way about this.

answered Oct 12 '12 at 11:17

Dirk Eddelbuettel

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vector permVector (perm, perm + sizeof(perm) / sizeof(perm[0]) ); Did the trick, thanks! – Datageek Oct 12 '12 at 11:23
Yes, `std::vector` also gets the implicit form of `Rcpp::wrap`. – Dirk Eddelbuettel Oct 12 '12 at 11:32
Also, more generally speaking, there is _no reason_ why you want an `int[]` array in 2012. The STL vector or the Rcpp vector are preferable (IMHO) on every count. – Dirk Eddelbuettel Oct 12 '12 at 12:15
That's the solution I found as a best way of initializing an STL vector: http://stackoverflow.com/a/2236227/328989 – Datageek Oct 12 '12 at 12:55
1

Right -- you can do a little better with C++11 (see eg [this Wikipedia article](http://en.wikipedia.org/wiki/C%2B%2B11#Initializer_lists)), also adding `-std=c++0x` to the `g++` flags. Mind you, CRAN would not allow that in an uploaded package but for local use it is just fine. – Dirk Eddelbuettel Oct 12 '12 at 13:05
In that case, you might want : `wrap( perm, perm + 3 )` – Romain Francois Oct 24 '12 at 07:16
Or perhaps `IntegerVector::create(2,1,3)` – Romain Francois Oct 24 '12 at 07:17

Passing attributes to Rcpp::Function

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