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!
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