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">
|
|
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--
Dirk Eddelbuettel | e...@debian.org | http://dirk.eddelbuettel.com
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