NA_REAL is just a NaN with a special value in the payload, so it's fine to use. Hadley
On Thu, Jun 2, 2016 at 7:07 AM, Jason Foster <jason.j.fos...@gmail.com> wrote: > Hi, > > My question is how can I return a thread safe NA_REAL using RcppParallel? > I've read many posts about how it's not thread safe to call R or Rcpp APIs > when using RcppParallel > (http://lists.r-forge.r-project.org/pipermail/rcpp-devel/2016-January/009061.html), > so in the past I've played it safe by returning NAN in C++ instead (as it's > my understanding NA_REAL is specific to R). > > The following example is a modified version of "Transforming a Matrix in > Parallel using RcppParallel" > (http://gallery.rcpp.org/articles/parallel-matrix-transform/) that checks > whether the input value is NA before taking the sqrt, otherwise NA is > returned (note: this is the desired behavior and for illustrative purposes > only): > > // [[Rcpp::depends(RcppParallel)]] > #include <Rcpp.h> > #include <RcppParallel.h> > using namespace Rcpp; > using namespace RcppParallel; > > struct SquareRoot : public Worker > { > // source vector > const RVector<double> input; > > // destination vector > RVector<double> output; > > // initialize with source and destination > SquareRoot(const NumericVector input, NumericVector output) > : input(input), output(output) {} > > // take the square root of the range of elements requested > void operator()(std::size_t begin, std::size_t end) { > for (std::size_t i = begin; i < end; i++) { > if (std::isnan(input[i])) { > output[i] = NA_REAL; // this is the desired output (instead of NAN) > } else { > output[i] = sqrt(input[i]); > } > } > } > }; > > // [[Rcpp::export]] > NumericVector parallelVectorSqrt(NumericVector x) { > > // allocate the output vector > NumericVector output(x.size()); > > // SquareRoot functor (pass input and output vectors) > SquareRoot squareRoot(x, output); > > // call parallelFor to do the work > parallelFor(0, x.size(), squareRoot); > > // return the output vector > return output; > > } > > Any guidance or insight would be much appreciated. Thanks! > > > > > > _______________________________________________ > Rcpp-devel mailing list > Rcpp-devel@lists.r-forge.r-project.org > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel -- http://hadley.nz _______________________________________________ Rcpp-devel mailing list Rcpp-devel@lists.r-forge.r-project.org https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
