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
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Romain Francois
Professional R Enthusiast
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