sum.cpp

/**
 * @title Summing a Vector in Parallel with RcppParallel
 * @author JJ Allaire
 * @license GPL (>= 2)
*/

#include<Rcpp.h>
#include<RcppParallel.h>

// [[Rcpp::depends(RcppParallel)]]
usingnamespaceRcppParallel;
usingnamespaceRcpp;

structSum : publicWorker
{
// source vector
const RVector<double> input;

// accumulated value
double value;

// constructors
Sum(const NumericVector input) : input(input), value(0) {}
Sum(const Sum& sum, Split) : input(sum.input), value(0) {}

// accumulate just the element of the range I have been asked to
voidoperator()(std::size_t begin, std::size_t end) {
 value += std::accumulate(input.begin() + begin, input.begin() + end, 0.0);
 }

// join my value with that of another Sum
voidjoin(const Sum& rhs) {
 value += rhs.value;
 }
};

// [[Rcpp::export]]
doubleparallelVectorSum(NumericVector x) {

// declare the SumBody instance
 Sum sum(x);

// call parallel_reduce to start the work
parallelReduce(0, x.length(), sum);

// return the computed sum
return sum.value;
}

// [[Rcpp::export]]
doublevectorSum(NumericVector x) {
returnstd::accumulate(x.begin(), x.end(), 0.0);
}