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

[Christian Gunning]

Sorry for slow reply.

> Or perhaps use the "_" thing :
>
> ret( i, _ ) = ...

Is there documentation on _?

> 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 ;


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

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
>
>
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> Romain Francois
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