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.
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">
>
>
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> Rcpp-devel@lists.r-forge.r-project.org
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>
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