Le 21/09/10 13:20, Christian Gunning a écrit :
On Tue, Sep 21, 2010 at 2:56 AM, Romain Francois
<rom...@r-enthusiasts.com> wrote:
Sure. I need to think a little bit more about how to do Rcpp::Array, etc
...
because an Array could have an arbitrary number of dimensions.
Perhaps embedding information into the class would work.
// make an array of 3 dimensions, etc ...
Rcpp::Array<3> ret( y ) ;
Maybe solving the just the 3D case instead of n-D solve the majority
of use cases?
Yes, I've been thinking similarly about an Indexer class. Accounting
for a variable number of dimensions looks unpleasantly messy.
Yes. Feel free to share thoughts on that.
Since an R-style mat(2,) is illegal, perhaps a simple solution is
using booleans in the index position to indicate "all", This solves
a decent range of use cases, and should be accessible to the "native
R" crowd. Here's a simple one:
NumericMatrix ret(inmat);
double lambda = as<double>(inlambda);
int nr = ret.nrows();
int nc = ret.ncols();
int i;
for (i=0; i<nr; i++) {
ret(i,true) = rpois(nc, lambda);
};
I don't like that. I'd rather go with a dummy class.
class Empty{} ;
and have something like this:
ret( i, Empty() ) = ...
Or perhaps use the "_" thing :
ret( i, _ ) = ...
Or perhaps have this syntax :
ret.row(i) = ...
We aleardy have row member function that returns a Row object, but it
currently does not have a operator=, that could be taken care of.
The next logical extension of matrix/array indexing beyond boolean
would be to allow NumericVectors in each of the index positions. At
this point, though, there's an explosion of over-loaded functions - a
3D Num myArray(x, y, z) gives 27 separate functions for x,y,z chosen
from {bool, int, NumericVector}, plus NumericMatrix and NumericVector.
Here's where an indexer class starts to make sense - unified
constructors, along with clear dimensionality of the indexer and
simple checks of dimensional conformance between indexer and indexed.
Sure.
As a side-note, I just spent some time with arma, and was sad to find
that arma_mat.insert_rows(atrow, rowvec) extends arma_mat, with no
apparent way to do row/col-level in-place replacement. So, at least
we're not whipping a dead horse.
Can you point me to the relevant NumericMatrix(i,j) indexer code?
Look for the "offset" member functions in
https://r-forge.r-project.org/scm/viewvc.php/pkg/Rcpp/inst/include/Rcpp/vector/Vector.h?view=markup&revision=2031&root=rcpp
This is what is used by operator()(int,int) in Matrix.h:
https://r-forge.r-project.org/scm/viewvc.php/pkg/Rcpp/inst/include/Rcpp/vector/Matrix.h?view=markup&revision=1907&root=rcpp
thanks much,
Christian
--
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30
http://romainfrancois.blog.free.fr
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