[Rcpp-devel] Sample function(s) for inclusion in RcppArmadillo

Perfect timing. Meant to email you yesterday regarding sample(), but that
fell off the hectic wagon. We should get back to this.

| I'm working on writing runit tests for the previously-discussed
| sample, and I just hit my competence threshold dealing with
| inst/include.
| As discussed, the (overloaded) sample() functions are to be called
| only from user C++ code and are thus not exposed to R.
| This means that the function definitions should go in inst/include, correct?

Yes.
 
| I don't really know what I'm doing here.  If someone could recommend a
| good reference for namespace control, headers, and R-package specific
| issues I'd be grateful.   Details follow:
| 
| I'm trying to get the following test function to use RcppArmadillo's
| definition of sample, and the compiler never finds it:

|     require(Rcpp)
|     cppFunction( code='
|         IntegerVector sample_int_noprob( IntegerVector x, int size,
| bool replace) {
|             RNGScope scope;
|             IntegerVector ret = RcppArmadillo::sample(x, size, replace);
|             return ret;
|         }',
|     depends='RcppArmadillo'
|     )

a) Is your #include file being loaded?  Did you add a statement to your copy
of RcppArmadillo.h or some other header file?  Else it is not included -- and
the compiler has no idea what you are talking about.  

b) If a) is taken care of, is sample() defined inside 'namespace armadillo' ?
 
| I tried placing the definition of sample in
| RcppArmadillo/inst/include/sample.h.
|         using namespace Rcpp;
|         template <class T>
|         T sample(const T &x, const int size, const bool replace,
| NumericVector prob_ = NumericVector(0) ) {
|             // Templated sample -- should work on any Rcpp Vector
|          ...
|         }

That would be a no to b).
 
| I've tried to use RcppArmadilloWrap.h as an example, using:
| namespace Rcpp{
|     namespace RcppArmadillo{
|     ...
|     }
| }

That would be two nested namespaces (which I don't we do for Armadillo) as in

     Rcpp::RcppArmadillo::sample()

You don't really have a stanza as we haven't defined other utility functions
for RcppArmadillo yet.   

If you have a simple clean diff we can maybe noodle over this this week.
Maybe you and should work on this off-list?

Dirk


| best,
| Christian
| 
|

| >

| > |     |     Also, you may need to add RNGScope() if you use R's RNG.
| > |     |
| > |     |
| > |     |
| > |     | Yes, I should have mentioned that in my post.  Calling RNGScope() is left
| > |     to
| > |     | the user, since multiple calls to sample() can conceivably happen inside
| > |     a
| > |     | single RNGScope().
| > |
| > |     With that, maybe best to be included as another example in RcppArmadillo ?
| > |
| > |
| > | Why?  The proposed behavior is the same as sugar's rnorm, etc.: a utility
| > | function that uses R's RNG -- it's the
| > | user's responsibility to properly scope the RNG.
| >
| > Fair point.
| >
| > | When time permits, I'll add Romain's comments on sugarizing sample (which I
| > | *think* I understand), along with some testing code.
| >
| > Excellent plan.
| >
| > Dirk
| >
| > --
| > Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com
| >
| >
| 
| 
| 
| -- 
| A man, a plan, a cat, a ham, a yak, a yam, a hat, a canal ? Panama!
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Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com