Yes it is the same question on SO and I did consider RHertel's comments. But this problem (sums by group id) is not parallelFor it is parallelReduce: I split vector, calculate sums and then aggregate those sums. Please correct me if I am wrong.
2015-07-14 13:54 GMT+03:00 Dirk Eddelbuettel <e...@debian.org>: > > On 14 July 2015 at 09:25, Danas Zuokas wrote: > | I have written parallel implementation of sums in groups using > RcppParallel. > > Isn't this the same question as > > http://stackoverflow.com/questions/31318419/when-calling-same-rcpp-function-several-times-different-results-are-returned > > You got some excellent comments there by SO user 'RHertel'. Did you > consider those? > > Dirk > > | // [[Rcpp::depends(RcppParallel)]] > | #include <Rcpp.h> > | #include <RcppParallel.h> > | using namespace Rcpp; > | using namespace RcppParallel; > | > | struct SumsG: public Worker > | { > | const RVector<double> v; > | const RVector<int> gi; > | > | RVector<double> sg; > | > | SumsG(const NumericVector v, const IntegerVector gi, NumericVector > sg): v(v), gi(gi), sg(sg) {} > | SumsG(const SumsG& p, Split): v(p.v), gi(p.gi), sg(p.sg) {} > | > | void operator()(std::size_t begin, std::size_t end) { > | for (std::size_t i = begin; i < end; i++) { > | sg[gi[i]] += v[i]; > | } > | } > | > | void join(const SumsG& p) { > | for(std::size_t i = 0; i < sg.length(); i++) { > | sg[i] += p.sg[i]; > | } > | } > | }; > | > | // [[Rcpp::export]] > | List sumsingroups(NumericVector v, IntegerVector gi, int ni) { > | NumericVector sg(ni); > | SumsG p(v, gi, sg); > | parallelReduce(0, v.length(), p); > | > | return List::create(_["sg"] = p.sg); > | } > | > | It compiles using Rcpp::sourceCpp. Now when I call it from > R sumsingroups(1:10, > | rep(0:1, each = 5), 2) several times I get the right answer (15 40) and > then > | something different (usually some multiplicative of the right answer). > Running > | > | > | res <- sumsingroups(1:10, rep(0:1, each = 5), 2) > | for(i in 1:1000) { > | tmp <- sumsingroups(1:10, rep(0:1, each = 5), 2) > | if(res[[1]][1] != tmp[[1]][1]) break > | Sys.sleep(0.1) > | } > | > | breaks at random iteration returning > | > | $sg > | [1] 60 160 > | > | or > | > | $sg > | [1] 30 80 > | > | I am new to Rcpp and RcppParallel and do not know what could cause such > | behavior. > | > | Things that did not help: > | > | 1. Added for (std::size_t i = 0; i < sg.length(); i++) sg[i] = 0; to > both of > | constructors. > | 2. Changed names so that they are different in Worker definition and in > | function implementation. > | > | _______________________________________________ > | 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://dirk.eddelbuettel.com | @eddelbuettel | e...@debian.org >
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