On 10 February 2012 at 15:56, Andy Leung wrote:
| Dear Rcpp users and developers,
|
| I understand how to extract a single column or row from an
| RcppArmadillo matrix, but I am still unsure how to extract columns or
I use span() methods a lot too, but thety are continuous...
| rows based on a vector of indices. I wrote a rather awkward (and dumb)
| way to extract, and here are some reproducible codes:
|
| ###############################
| library(Rcpp)
| library(RcppArmadillo)
| library(inline)
| src <-
| ' arma::mat x = arma::randu(5, 5);
| arma::mat y = x;
| arma::uvec indice;
| indice << 0 << 3;
| int nRm = indice.n_elem;
| for(int j = 0; j < nRm; j++)
| y.shed_col( indice(j) - j );
| return List::create(Named("x")=x, Named("y")=y, Named("ind")=indice);'
| colX <- cxxfunction(body=src,plugin="RcppArmadillo")
| colX()
| ###############################
|
| Although this code works, I am wondering if there are other more
| clever ways of approaching this, especially a way to avoid any 'for'
| loops.
Not that I know off. It's an area ripe for further contributions....
Dirk
|
| Thank you for your help!
| Andy Leung
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