On 19 November 2012 at 09:31, Hadley Wickham wrote: | Hi all, | | Inspired by "Rcpp is smoking fast for agent-based models in data | frames" (http://www.babelgraph.org/wp/?p=358), I've been doing some
[ I liked that post, but we got flak afterwards as his example was not well chosen. The illustration of the language speed difference does of course hold. ] | exploration of vectorisation in R vs C++ at | https://gist.github.com/4111256 | | I have five versions of the basic vaccinate function: | | * vacc1: vectorisation in R with a for loop | * vacc2: used vectorised R primitives | * vacc3: vectorised with loop in C++ | * vacc4: vectorised with Rcpp sugar | * vacc5: vectorised with Rcpp sugar, explicitly labelled as containing | no missing values | | And the timings I get are as follows: | | Unit: microseconds | expr min lq median uq max neval | vacc1(age, female, ily) 6816.8 7139.4 7285.7 7823.9 10055.5 100 | vacc2(age, female, ily) 194.5 202.6 212.6 227.9 260.4 100 | vacc3(age, female, ily) 21.8 22.4 23.4 24.9 35.5 100 | vacc4(age, female, ily) 36.2 38.7 41.3 44.5 55.6 100 | vacc5(age, female, ily) 29.3 31.3 34.0 36.4 52.1 100 | | Unsurprisingly the R loop (vacc1) is very slow, and proper | vectorisation speeds it up immensely. Interestingly, however, the C++ | loop still does considerably better (about 10x faster) - I'm not sure | exactly why this is the case, but I suspect it may be because it | avoids the many intermediate vectors that R requires. The sugar | version is about half as fast, but this gets quite a bit faster with | explicit no missing flags. | | I'd love any feedback on my code (https://gist.github.com/4111256) - | please let me know if I've missed anything obvious. I don't have a problem with sugar being a little slower that hand-rolling. The code is so much simpler and shorter. And we're still way faster than vectorised R. I like that place. Somewhat off-topic/on-topic: I am still puzzled by how the Julia guys now revert back from vectorised code to hand-written loops because llvm does better on those. Speed is good, but concise code with speed is better in my book. Hence I would prefer to invoke the 80/20 rule as I think we have better targets to chase than to narrow that gap. But that's just my $0.02... If you can't sleep til both version have 20-some microsend medians then by all means go crazy ;-) Dirk -- Dirk Eddelbuettel | e...@debian.org | http://dirk.eddelbuettel.com _______________________________________________ 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
