Hello all, I?ve been working with R for some years, but I am beginner to Rcpp (and have no experience with C++). I am trying to set zeros in a matrix to Inf. In R I would do this: x=matrix(8:0,3) x[which(x==0)]=Inf My try with Rcpp and RcppArmadillo looked like this (as I do not know how it works with inf I just set it to 100 in a first step): library(Rcpp) library(inline) library(RcppArmadillo) code <- ' arma::mat M0 = Rcpp::as<arma::mat>(a); arma::mat M1 = Rcpp::as<arma::mat>(a); arma::uvec xx = find (M1==0); M1(xx)=100; M1=M0+M1; return Rcpp::wrap(M1); ' tf <- cxxfunction(signature(a="numeric"), code,plugin="RcppArmadillo") tf(x) But this just produces errors *? However, setting the index ?manually? would work (changing M1(xx)=100 to M1(8)=100). What do I have to change to make it work? If I understood it correctly, it should be possible to use inf (http://arma.sourceforge.net/docs.html&constants). Can I do this simply by setting M1(xx)=inf; ? Thanks to anyone who takes the time to answer my questions. Best wishes, Karin * They are long and (I think) not very informative. But I can provide them if requested.