Hey Ralf, You are right. In the past, when I have had to have a lot of explanation, that generally points to me lacking understanding.
After reading your example again with your explanation, it seems clear that I can transition to RcppParallel. I will respond back here with an update. I really appreciate all of the help/patience and sorry for the many rookie mistakes. Joseph Wood On Fri, Sep 28, 2018 at 6:00 AM <rcpp-devel-requ...@lists.r-forge.r-project.org> wrote: > > Send Rcpp-devel mailing list submissions to > rcpp-devel@lists.r-forge.r-project.org > > To subscribe or unsubscribe via the World Wide Web, visit > > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel > > or, via email, send a message with subject or body 'help' to > rcpp-devel-requ...@lists.r-forge.r-project.org > > You can reach the person managing the list at > rcpp-devel-ow...@lists.r-forge.r-project.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Rcpp-devel digest..." > > > Today's Topics: > > 1. Re: Populate a Matrix in Parallel (Text Version) (Ralf Stubner) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Fri, 28 Sep 2018 11:07:49 +0200 > From: Ralf Stubner <ralf.stub...@daqana.com> > To: rcpp-devel@lists.r-forge.r-project.org > Subject: Re: [Rcpp-devel] Populate a Matrix in Parallel (Text Version) > Message-ID: <d1c66c37-3c6a-fb4a-0955-2af891080...@daqana.com> > Content-Type: text/plain; charset="utf-8" > > Hi Joseph, > > On 9/28/18 3:26 AM, Joseph Wood wrote: > > I understand that parallelism is not a magic wand. Have you read my > > original post? I have managed to parallelize generating permutations > > by taking advantage of the fact that I can generate the ith > > permutation via nthPerm. My question is about making this thread safe > > not if it is possible. > > unfortunately, you messages are a bit long and contradictory. I had the > same reaction as Jeff when I read > > >> My situation is fundamentally different. The algorithm that fills the > >> matrix does so in a way that relies on the previous row and more > [...] > > If you have code that generates the n-th row based on some global input, > then the example I refered to would be the right starting point. It uses > global state (seed) and column indices to fill a matrix by column. It > does it for multiple columns together, since it is more efficient to > have one thread process multiple columns. However, the default grain > size for parallelFor is one, so it is easy to create one thread per > column and perform some action based on some global input and on the > column index: > > > #include <Rcpp.h> > // [[Rcpp::depends(RcppParallel)]] > #include <RcppParallel.h> > // [[Rcpp::plugins(cpp11)]] > > struct ParallelFill : public RcppParallel::Worker { > RcppParallel::RMatrix<double> output; > RcppParallel::RVector<double> global_input; > > ParallelFill(Rcpp::NumericMatrix output, > Rcpp::NumericVector input) : > output(output), global_input(input) {}; > > std::vector<double> create_column(std::size_t index) { > std::vector<double> result(global_input.size()); > std::transform(global_input.begin(), > global_input.end(), > result.begin(), > [&index] (double a) {return a + index;}); > return result; > } > > // default grain size is 1, i.e. end == begin + 1 > void operator()(std::size_t begin, std::size_t end) { > std::vector<double> column = create_column(begin); > std::copy(column.begin(), column.end(), > output.begin() + begin * output.nrow()); > } > }; > > // [[Rcpp::export]] > Rcpp::NumericMatrix parallel_matrix(const int n, > Rcpp::NumericVector input) { > Rcpp::NumericMatrix res(input.length(), n); > ParallelFill parallelFill(res, input); > RcppParallel::parallelFor(0, n, parallelFill); > return res; > } > > /*** R > set.seed(42) > res <- parallel_matrix(8, runif(1e7)) > head(res) > */ > > All this is done *by column*, since matrices in R are stored that way. > > cheerio > ralf > > > -------------- next part -------------- > A non-text attachment was scrubbed... > Name: signature.asc > Type: application/pgp-signature > Size: 833 bytes > Desc: OpenPGP digital signature > URL: > <http://lists.r-forge.r-project.org/pipermail/rcpp-devel/attachments/20180928/fb0a9e04/attachment-0001.sig> > > ------------------------------ > > Subject: Digest Footer > > _______________________________________________ > 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 > > ------------------------------ > > End of Rcpp-devel Digest, Vol 107, Issue 17 > ******************************************* _______________________________________________ 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
