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    <p>Well there is the good old <em>Use the source, Luke!</em> --- R itself has plenty of (very efficient) C code one can study, and CRAN has hundreds of packages, some from authors you trust. That provides real, tested examples to study and adapt.</p> <p>But as Josh suspected, I lean more towards C++ and hence <a href="http://dirk.eddelbuettel.com/code/rcpp.html" rel="noreferrer">Rcpp</a>. It also has plenty of examples.</p> <p><em>Edit:</em> There were two books I found helpful:</p> <ul> <li>The first one is Venables and Ripley's "<em>S Programming</em>" even though it is getting long in the tooth (and there have been rumours of a 2nd edition for years). At the time there was simply nothing else.</li> <li>The second in Chambers' "<em>Software for Data Analysis</em>" which is much more recent and has a much nicer R-centric feel -- and two chapters on extending R. Both C and C++ get mentioned. Plus, John shreds me for what I did with <a href="http://cran.r-project.org/package=digest" rel="noreferrer">digest</a> so that alone is worth the price of admission.</li> </ul> <p>That said, John is growing fond of <a href="http://dirk.eddelbuettel.com/code/rcpp.html" rel="noreferrer">Rcpp</a> (and contributing) as he finds the match between R objects and C++ objects (via <a href="http://dirk.eddelbuettel.com/code/rcpp.html" rel="noreferrer">Rcpp</a>) to be very natural -- and ReferenceClasses help there.</p> <p><em>Edit 2:</em> With Hadley's refocussed question, I <em>very strongly</em> urge you to consider C++. There is so much boilerplate nonsense you have to do with C---very tedious and <em>very avoidable</em>. Have a look at the <a href="http://dirk.eddelbuettel.com/code/rcpp/Rcpp-introduction.pdf" rel="noreferrer">Rcpp-introduction vignette</a>. Another simple example is <a href="http://dirk.eddelbuettel.com/blog/2010/09/07#straight_curly_or_compiled" rel="noreferrer">this blog post</a> where I show that instead of worrying about 10% differences (in one of the Radford Neal examples) we can get <em>eightyfold</em> increases with C++ (on what is of course a contrived example).</p> <p><em>Edit 3:</em> There is complexity in that you may run into C++ errors that are, to put it mildly, hard to grok. But to just <em>use Rcpp</em> rather than to extend it, you should hardly ever need it. And while this <em>cost</em> is undeniable, it is far eclipsed by the <em>benefit</em> of simpler code, less boilerplate, no PROTECT/UNPROTECT, no memory management etc pp. Doug Bates just yesterday stated that he finds C++ and Rcpp to be much more like writing R than writing C++. YMMV and all that.</p>
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    1. POWhere can I learn how to write C code to speed up slow R functions?
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    1. USDirk Eddelbuettel
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    1. COI expected I'd get a "use Rcpp" answer ;) It would be really useful if you could spell out the disadvantages of using C++ instead of C. One major one would seem to be that C++ is much more complex that C - does this make it harder to use? (Or in practice, can you write C++ code that's very similar to C?) I would also appreciate more reference material that's aimed at new users who are not familiar with the existing C api.
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    2. COSee *Edit 3* and *yes, you can*. Meyers calls C++ a 'four paradigm' language and you do not have to use all four. Using it as 'just a better C' and use Rcpp as glue to R is perfectly fine. Nobody forces a style on you -- this ain't Java ;-)
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    3. CO@Dirk: thx for the elaboration. It raised the question in our office before, as C is commonly used here instead of C++. When would the use of C over C++ beneficial, or do you simply say "never C, always C++"?
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