Le 04/05/10 22:26, Douglas Bates a écrit :
In the files src/MatrixNs.{h,cpp} of the lme4a package (the
development version of lme4, available only from R-forge) I create C++
classes that parallel some of the S4 classes in the Matrix package for
R. Most of the time I apply operations in those classes to numeric
vectors passed as arguments or components of arguments from R. Thus
many of the function signatures include arguments of the form
NumericVector const&
If I have a more complex operation to perform in C++ using temporary
storage I could allocate the storage by declaring
NumericVector bar(foo.size());
or something like that, even though this vector will never be touched
by R. I think this is the simplest approach so that I only need to
use one set of function signatures in the MatrixNs.h declarations.
Alternatively I could declared multiple function signatures for both
NumericVector const& and std::vector<double> const& arguments and
allocate the temporary storage using std::vector<double> instead of
NumericVector.
Or I could even declare all the function arguments as
std::vector<double> const& and convert the NumericVector objects to
that form (although I think that might involve some copying) before
passing them.
yes
I am currently favoring using NumericVector to allocate the
temporaries, even though the storage must be allocated and freed
through R's mechanisms.
Opinions?
It depends what you do with the data. If you change the size of the
vector from time to time, add elements, remove elements, I'd go for
std::vector.
For fixed size, I'd use R(cpp) data structures, which perform just as
good as std::vector, both really are glorified C arrays. And then you
have the option of returning the data to R cheaply.
One other way if you really wanted to use std::vector would be to wrap
them in external pointers. but that's a bit more work.
--
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30
http://romainfrancois.blog.free.fr
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