[Rcpp-devel] Filling NumericMatrix with NumericVectors with apply by row/column?

[Romain Francois]

Le 05/10/10 11:16, Christian Gunning a écrit :
> Sorry for slow reply.
>
>> Or perhaps use the "_" thing :
>>
>> ret( i, _ ) = ...
>
> Is there documentation on _?

No.

It is used in a few places :

Function rnorm( "rnorm" ) ;
rnorm( 10, _["mean"] = 2.0 ) ;

Language call( "rnorm", _["sd"] = 3.0 ) ;

List::create(
   _["foo"] = 3,
   _["bar"] = "bla" ) ;

>> 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.
>
> This sounds good.
> I'll look at this in the next week or 2.
>
> Two questions about how this might extend -
>
> 1.  Would this allow for an analogous member function along the
> following lines, or is "Rows" too much of a stretch?
>
> typedef MatrixRows<RTYPE>  Rows ;
> inline Rows row( NumericVector i ){ return Row( *this, i ) ; }
>
> and
>
> Class MatrixRows :
>      ...
>      private:
>          MatrixRow&  row ;
>          NumericVector index ;

I'm not sure. What would you then do with a "Rows" object ?

> 2. For an Array class, does a chained assignment like
> ret.slice(i).row(j) = ... sound sensible?

That implies that Array is only 3D. This surely is most of the cases, 
but I don't want to impose the restriction.

Chaining might be possible, with some work.

> best,
> xian
>
>>> 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
|- http://bit.ly/cCmbgg : Rcpp 0.8.6
|- http://bit.ly/bzoWrs : Rcpp svn revision 2000
`- http://bit.ly/b8VNE2 : Rcpp at LondonR, oct 5th