Rcpp sugar for NumericMatrix

Question

For NumericVector, I can subset a smaller NumericVector by using an IntegerVector that contains the positions to subset.

e.g. suppose x<-c(1,2,2,3,4,5), idx<-c(1,3,4), and xsub<-x[idx] which is 1 2 3.

Within RCpp, I can simply use xsub=x[idx].

Is there a similar way to subset the rows of a NumericMatrix using the IntegerVector?

For example, the following code xmatsub=xmat(idx,_) didn't work for me.

Answer 1

There isn't a way. You have to do it manually, which is not that complicated.

NumericMatrix res( idx.size(), m.rows() )  ;
for( int i=0; i<idx.size(); i++){
    res.row(i) = m.row(idx[i]-1) ; 
}