[Rcpp-devel] Basic documentation for Rcpp

Dirk Eddelbuettel edd at debian.org
Fri May 13 15:45:04 CEST 2011


On 13 May 2011 at 15:02, Nick Sabbe wrote:
| Hello all.
| Today, I posted a question on stackoverflow.com, but I was advised to ask the
| question through this mailing list.

That is indeed frequently suggested by Romain and myself, and I am glad that
others suggested it to you to.  With that, thanks for posting here.
| So, here is the verbatim question from SO (http://stackoverflow.com/questions/
| 5991314/basic-documentation-for-rcpp):

I took a few minutes and quickly edited a reply over there.  I will repost it
here later if nobody beats me to answering your questions.  Below are just
some additional real quick answer.

I really suggest that you make an effort of re-reading Rcpp-introduction
which answers some of the questions below.,
| I want to look into rcpp to improve the speed of some of my R code without
| having to resort to messy C++ code (I've had some success with that, but it
| looks like code from hell).
| So, I checked the documentation provided with Rcpp, and also the bundle of
| documents provided at Dirk Eddelbuettel's site. I installed and looked at
| RcppExamples, but (at least from its documentation) most of these refer to
| RcppClassic?. Besides that, I did some googling but that didn't result in
| answers to what seem like basic questions.
| ?         Do indexes in Rcpp work zero-based or one-based

Zero-based as are all C and C++ programs (unless you do something crazy and
redefine things).  We do not attempt to change C++.
| ?         List provides both operator() and operator[], but apparently
| not operator[[]]. It is not clear which ones are similar to [] and [[]] in R.

There cannot be.  We are bound by what C++ lets us do.  Likewise there is no
matrix indexing  M[i][j] -- it has to be M(i,j).
| ?         Is there any support for factors in Rcpp (there does not appear to be
| any)?

It is on the TODO list but low priority for us. Export the factor levels as
character, and the factor values via as.integer.   Contributions of a
Rcpp::Factor class would welcome.


| Note: in fact I found some answers from the first example in
| Rcpp-introduction.pdf, but that just felt like luck.
| Also, my stl is very rusty, so if anybody can provide me with a simple example
| where each element of a List is (e.g.) print-ed with an stl-style loop, that
| would be neat.
| If anybody wants to call me an idiot for not finding this information: go ahead
| and make your day. Then make mine and point me to the docs I need :-)
| As a suggestions to Mr. Eddelbuettel and other Rcpp authors (I expect some of
| them to read this): the class hierarchies and the like, provided by doxygen,
| are really neat when you are already kneedeep into Rcpp, but for a beginner (in
| Rcpp), I am more interested in a list of 'this method in this class does this
| like that function in R' rather than 'you can find the declaration of this
| operator in this header file'. After all, I understand one of the goals of Rcpp
| is to lower the threshold for using C++ in R? Note: from what I have seen and
| understood, I highly value the actual code of Rcpp and have the highest respect
| for its creators. If the lack of basic documentation is merely a result of
| 'lack of resources', I would be willing to become a resource (e.g.: work on
| 'basic' documentation once I get through it myself).
| Nick Sabbe
| --
| ping: nick.sabbe at ugent.be
| link: http://biomath.ugent.be
| wink: A1.056, Coupure Links 653, 9000 Gent
| ring: 09/264.59.36
| -- Do Not Disapprove
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