C-Side: Applying a function (given as param) to data (given as param)
On Fri, Jun 3, 2011 at 5:17 AM, oliver <oliver at first.in-berlin.de> wrote:
Hello, I'm implementing a package (C-extension), where one function gets data and a function that needs to be applied to the data. I want to apply the function to (parts of) the data on the C-side. 1) how do I apply a function (given via SEXP) to data 2) how do I select parts of the data (also provided via SEXP)?
Not to be facetious but you begin by reading the "Writing R Extensions" manual. An alternative is to read the vignette Rcpp-Introduction available as http://dirk.eddelbuettel.com/code/rcpp/Rcpp-introduction.pdf and soon to be in The R Journal. They show an explicit example of apply in compiled code (C++ using the Rcpp structures, in their case).
Comment on 2: I want to implement a moving/rolling/running apply on the data, so I want to select a data window. How can this be done, and how can it be done efficiently? For example on page 101 of "Writing R extensions" there was a trick on how to use REAL on the result, before using it in a loop. Can this be used for efficiency reasons in general? ?Ciao, ? ?Oliver P.S.: What do these macros (like REAL()) do? Do they convert data ? ? ?or rather cast datatypes?
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