There is a sleazy hack which works, but wastes a fair amount of memory:
take the transpose of the matrix in R, and use the fact that the columns of
that transpose are the rows of the original.
On Mon, Feb 18, 2013 at 5:37 PM, Dirk Eddelbuettel <e...@debian.org> wrote:
>
> On 18 February 2013 at 17:02, Kevin Ushey wrote:
> | One solution: X.row(ii) is actually generating a CharacterMatrix::Row ;
> ie, a
> | view of that row in the CharacterMatrix, and I think you need to
> explicitly
> | copy it to a CharacterVector and then assign that CharacterVector to the
> list.
> |
> | You could write something like:
> |
> | src <- '
> | CharacterMatrix X(XX_);
> | int Nx = X.nrow();
> | List ans;
> | for (int ii=0; ii<Nx; ii++) {
> | CharacterMatrix::Row view = X.row(ii);
> | CharacterVector tmp = no_init( X.ncol() );
> | for( int j=0; j < X.ncol(); j++ ) {
> | tmp[j] = view[j];
> | }
> | ans.push_back( tmp );
> | }
> | return(wrap(ans));
> | '
> |
> | although it is a bit clunkier. I'm not sure if there's a more idiomatic
> method
> | available.
>
> I think all approaches have to be clunky as all our data structures store
> column-wise, because that is what R does.
>
> So I would probably start by element-wise copying, see if that works / if
> that is fast enough and leave it at that.
>
> Dirk
> |
> | FWIW, trying to copy and assign directly, e.g. 'CharacterVector tmp =
> X.row
> | (ii);', doesn't seem to work, even though the same code works (and is in
> the
> | quick-start vignette) for NumericVector.
> |
> | -Kevin
> |
> | On Mon, Feb 18, 2013 at 3:37 PM, Søren Højsgaard <sor...@math.aau.dk>
> wrote:
> |
> | I want to split a matrix by its rows into a list as:
> | > a<- matrix(letters[1:6],ncol=2)
> | > split(a,row(a))
> | $`1`
> | [1] "a" "d"
> |
> | $`2`
> | [1] "b" "e"
> |
> | $`3`
> | [1] "c" "f"
> |
> | I do as follows and get a strange result. Any suggestions?
> |
> | Thanks in advance!
> | Søren
> |
> | ---------------
> |
> | src <- '
> | CharacterMatrix X(XX_);
> | int Nx = X.nrow();
> | List ans;
> | for (int ii=0; ii<Nx; ii++){
> | ans.push_back(X.row(ii));
> | }
> | return(wrap(ans));
> | '
> | split_ <- cxxfunction(signature(XX_="matrix"), plugin="Rcpp",
> body=src)
> |
> | split_(a)
> |
> | [[1]]
> | [[1]][[1]]
> | <CHARSXP: "a">
> |
> | [[1]][[2]]
> | <CHARSXP: "d">
> |
> |
> | [[2]]
> | [[2]][[1]]
> | <CHARSXP: "b">
> |
> | [[2]][[2]]
> | <CHARSXP: "e">
> |
> |
> | [[3]]
> | [[3]][[1]]
> | <CHARSXP: "c">
> |
> | [[3]][[2]]
> | <CHARSXP: "f">
> |
> |
> | _______________________________________________
> | Rcpp-devel mailing list
> | Rcpp-devel@lists.r-forge.r-project.org
> |
> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
> |
> |
> |
> | ----------------------------------------------------------------------
> | _______________________________________________
> | Rcpp-devel mailing list
> | Rcpp-devel@lists.r-forge.r-project.org
> | https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
> --
> Dirk Eddelbuettel | e...@debian.org | http://dirk.eddelbuettel.com
> _______________________________________________
> Rcpp-devel mailing list
> Rcpp-devel@lists.r-forge.r-project.org
> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
>
_______________________________________________
Rcpp-devel mailing list
Rcpp-devel@lists.r-forge.r-project.org
https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
