[Rcpp-devel] subsetting a matrix

[Hideyoshi Maeda]

Hi Rcpp-devel list,

I would like to subset a matrix by only selecting certain rows.

Something like the below…where y is a vector of integers that represent the rows to be selected. However the below does not seem to work.

// [[Rcpp::export]]
Rcpp::NumericMatrix ss(SEXP X_,SEXP y_){
  Rcpp::NumericMatrix X(X_)
  Rcpp::NumericVector y(y_)
  return X[y];
}

R> ss(matrix(rnorm(90),ncol=3),c(1,5,12,22))

It is a bit similar to this question http://stackoverflow.com/questions/13038256/subset-of-a-rcpp-matrix-that-matches-a-logical-statement however rather than just a single value, the find it for a vector.

also I am not too sure to what extent the Armadillo submat function is able to say subset for example rows: 1,5, 12 and 22 and then call the resulting matrix something else?

I was hoping that this subsetting procedure was going to be easy…but I seem to have got stuck.

thanks

HLM

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