Great! Thank you, Hadley. On Jun 2, 2016 7:30 AM, "Hadley Wickham" <h.wick...@gmail.com> wrote:
> 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 >
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