[Rcpp-devel] Rcpp-devel Digest, Vol 14, Issue 17

[Christian Gunning]

On Sat, Dec 4, 2010 at 7:35 AM,
<rcpp-devel-request at lists.r-forge.r-project.org> wrote:
> While I am on this, would it be valuable to have something like this:
>
> typedef SubMatrix<REALSXP> NumericSubMatrix ;
>
> or perhaps inside Matrix we could have:
>
> typedef typename SubMatrix<RTYPE> sub ;
>
> So that we would write
>
> NumericMatrix::sub yy = xx( Range(0,2), Range(0,3) )

Looks nice.  I was wondering about that.

Question -

Is there a simple example where the following differ?  I looked at the
source, and it looks to me that MatrixColumn, MatrixRow, and SubMatrix
objects are still tied to the original Matrix object (example 1),
whereas example 2 creates an entirely new object.  I don't understand
the exact consequences of this.  Am I correct in assuming that A, 1
does not make a new copy, and that B, modifications to the SubMatrix
object propogate back to the underlying Matrix?

1) NumericMatrix::sub yy1 = xx( Range(0,2), Range(0,3) )

2) NumericMatrix: yy2 = xx( Range(0,2), Range(0,3) )

thanks,
Christian

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