[Rcpp-devel] RFC -- Function for making modules ala inline

Christian,

Thanks for (re-)posting this. Do you have an example use with an example
module, or maybe with one of the unit tests?

Not the most minimal example, but it should give you some idea...

## begin example
mm1= matrix(1:40, ncol=10) +0.001;
mm2= matrix(1:20, ncol=10) +0.001
require(inline)
source('modfunction.R.txt');
dd3 = modfunction('mdist', 'Dist.cpp.txt', plugin='Rcpp', verbose=F)
dtest = new(dd3$Dist,  mm1, mm2)
tt = list()
tt$d2 = ( (dtest$dist( 2)[,1]) -  as.matrix(dist(rbind(mm2[1,], mm1)))[-1,1])
tt$d1 = ( dtest$dist( 1)[,1] -  as.matrix(dist(rbind(mm2[1,], mm1),
method='minkowski', p=1))[-1,1])
print(tt)


I have one question about the intended behavior of object persistence
here -- i.e. if i quit, save session, restart session, I can cause a
segfault with:

dtest = new(dd3$Dist,  mm1, mm2)

Does this indicate that I'm missing an on.exit() somewhere?

When I started with RcppBDT I did use cxxfunction() via its include=txt
argument but I haven't done much that way. ?I won't have a lot of time poking
around to see if this could / should be made better but I'll try to play with
it.

includes=txt gives the user a way to add *more* code to the body.  As
I see it, the salient issue here is that a module doesn't need any of
the "function wrapper" code, and doesn't return a function.  This is
why it's almost a proper subset of cxxfunction.

Not sure about the natural place for it. ?Some part of me sees it as an
extension / variant of cxxfunction -- which already has a weak dependency on
Rcpp via the plugin call.

One thought is  cxxfunction(plugin="RcppModule") -- a simple
if(plugin==)  in cxxfunction.  Then (i think) minimal modification
would be required:
    code <- sprintf('//no function defs \n\n %s ', modulecode)
and
    dyn.load(libLFile)
    retmod <- Module(modname, PACKAGE=f)
    return(retmod)


I'll try to look at this more, too, just wanted some confirmation that
I'm headed in a reasonable direction :)
-xian
-------------- next part --------------
using namespace Rcpp;
class Dist {
    public:
        Dist( NumericMatrix data_, NumericMatrix query_): 
            // data matrix of obs by row, query is a matrix of "row-obs"
            data(data_), nr(data_.nrow()), nc(data_.ncol()) {
                // add query and check that dimensions match
                set_query(query_);  
        }

        // only data is public (and is constant)
        const NumericMatrix data;
        
        NumericMatrix dist( double L_ ) {
            NumericMatrix ret(nr, nrq);  // one row per data obs, one col per query obs
            L = L_;
            for ( int rd=0; rd < nr; rd++) {
                for ( int rq=0; rq<nrq; rq++) {
                    ret(rd, rq) = distfun(rd, rq);
                }
            };
            return ret;
        }
        
        // query get/set
        NumericMatrix get_query() { return query;}
        void set_query(NumericMatrix query_) {
            query = query_;
            nrq = query.nrow();  // # of query obs
            if (nc != query.ncol()  ) throw std::length_error("Number of columns of data and query must match");
        }

    private:
        const int nr, nc;   // dimensions of data
        int nrq;            // dimensions of query, can vary
        double L;           // L-norm dimension
        NumericMatrix query;

        // dist for these rows of data and query
        double distfun(int rd, int rq) {    
            double ret = 0;
            for (int cc = 0; cc < nc; cc++) {  // column is "dimension"
                ret += pow ( fabs( 
                                    data( rd, cc) - query( rq, cc) 
                ), L);
            }
            ret = pow( ret, (1.0/L));
            //return pow( ret, (1.0/L) );
            return ret;
        }
};

RCPP_MODULE(mdist) {
    /* R usage:
        Dist <- Module("mdist")
        newdist <- new( Dist, matrix(1:100, ncol=10), matrix(1:20, ncol=10))
        newdist$dist(2) ## Euclidean distance
        show(newdist$dist)  ## introspect
    */
    class_<Dist>("Dist")
    .constructor<NumericMatrix, NumericMatrix>("\n  USAGE: \n\t newdist <- new( Dist, matrix(1:100, ncol=10), matrix(1:20, ncol=10)) \n -- Number of columns must match.")
    .field_readonly("data", &Dist::data, "Data is read-only.  Number of columns must match for data and query")
    .property("query", &Dist::get_query, &Dist::set_query, "Query can be modified.  Number of columns must match for data and query")
    .method("dist", &Dist::dist, "e.g. mydist$dist( 2 ); -- Euclidean distance")
    ;
}