Thanks again! On Sun, Jan 30, 2011 at 4:16 PM, Dirk Eddelbuettel <e...@debian.org> wrote:
> > Howdy, > > Thanks for posting here, and the kind words below. > > On 30 January 2011 at 15:49, Sunny Srivastava wrote: > | Dear Rcpp-List: > | > | I have been working on speeding my R code. A while ago, I realized that > no > | further vectorization would help and interacting R with C/C++/.. was > absolutely > | necessary. I don't program in C/C++ extensively, so the transition was a > | difficult process. I tried to use the R API but the error messages were > | intimidating. A few weeks ago I saw Professor Chambers presentation (pdf > from > | David Smith's website) about R in Stanford. I saw him mentioning Rcpp > which > | motivated me to try Rcpp (I confess, I am lazy to try new stuff). And I > haven't > | been dissapointed. Thank you very much Dirk and Romain (and other > developers, > | including Professor Chambers and Professor Bates). > | > | Rcpp reduced the length of my code considerably (like: I didn't need to > bother > | about PROTECT .. ) and the informative syntax (like: Rcpp::IntegerMatrix > ..) > | made my code more readable. These are great advantages, but the best part > was > | testing and compiling with the Inline package. I am a statistician; > writing a C > | program and then using dyn.load was the way I learned to do it in grad > school. > | Rcpp + inline makes this process way easier. > | > | Thank you for the great documentation on your webpage Dirk. It helped me > a lot. > | > | I am still a beginner in using Rcpp and friends (2 weeks old) and have a > few > | miscellaneous questions. The answer to these questions may be very basic > or > | obvious, so please bear with me. (Dirk showed me a simple way to test > things > | using Rcpp + inline here -- > http://stats.stackexchange.com/questions/6690/ > | > what-is-the-difference-between-rf-dpois-in-rmath-h-and-the-dpois-that-i-use-direc > | ) > | > | 1. I have been using Rcpp + inline to test if the faster implementation > gives > | the right results (which is obtained from R code). I was wondering if > there are > | other strategies which people use to test their Rcpp code? (sorry, if > this > | doesn't make sense.) > > No, that is precisely the best way about it: write code, and then test and > profile it. > > A few times in the past users have posted things here that lead us to > improve > things down the road. One only finds bottlenecks by testing for them. > > | 2. I have a MCMC simulation (say: foo) which uses several functions (say: > fun1, > | fun2). These functions (fun1, fun2) are themselves computation intensive > and I > | used Rcpp to speed them. Until now I do something like this: > | > | In R file: > | > | foo <- function (...){ > | > | src1 <- paste(readLines("fun1-rcpp.cpp"), collapse="\n") > | RcppFun1 <- cxxfunction( .., plugin="Rcpp",body=src1) > > You probably want to write a package. That way the 'compilation cost' is > borne just once when you install the package, rather than each time its > run. > > Doing a package may be a new step, but we try to help with documentation > and > existing packages. Give it a try! > > | ## similar cpp code for fun2 > | > | for (i in 1:10000){ > | ## use RcppFun1, RcppFun2 here > | } > | } > > It's a bit hard to say based on just this, but yes, you may be able to > 'refactor' this and regroup functions. But no need to obsess over it. > > | I was wondering if this is OK (it already speeds up my code by zillion > times) > | or is there a more elegant way of doing this. I am thinking about using > Rcpp to > | increase the speed of foo (for more speed) but I am not too sure on how > to do > | this. Towards this end, I checked a few packages mentioned on Dirk's > website > | namely, pcaMethods. I am thinking RcppExport and .Call is the way to do > this? > > Yes. Give it try, look at some small packages and try to copy whatever > package structure you may find useful. > > Cheers, Dirk > > > | Thank you for your answers or pointers. > | > | S. > | > | ---------------------------------------------------------------------- > | _______________________________________________ > | 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 > > -- > Dirk Eddelbuettel | e...@debian.org | http://dirk.eddelbuettel.com >
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