The most inefficient part I see is the creation of a new NumericVector inside the inner most loop. You copied each column n times, of which n-1 times are unnecessary.
Yan Zhou On Feb 19, 2013, at 11:02 PM, Dirk Eddelbuettel <e...@debian.org> wrote: > > Ken, > > On 19 February 2013 at 22:35, Ken Williams wrote: > | I have a need to loop through all the entries of a DataFrame by row, then > | column. I know two different ways: > > There have been prior discussions of this topic, as well as example posts -- > even leading to a Rcpp Gallery article. Did you read any of these? It wasn't > clear from your post. > > | I?m also curious why it?s a syntax error in Case A to just write `df[j][i]` > or > > Eeeek. I prefer the more C++-y way of writing df(j,i). Square brackets only > work for vectors, and even then you may be better off with x(i) for > consistency. > > Overall, your premise may be wrong too. "We all know" that a data.frame is > not the fastest data structure in R, so by forcing ourselves to the same > access are we not handycapping ourselves. > > Once you are in C++, you can use whatever C++ datatype you like. A > data.frame really is just a list of vectors, each of the vectors has eg a > begin(0 iterator which you can (fairly costlessly) instantiate STL types. > > And those give you performance guarantees. > > Hope this helps, Dirk > > -- > Dirk Eddelbuettel | e...@debian.org | http://dirk.eddelbuettel.com > _______________________________________________ > Rcpp-devel mailing list > Rcpp-devel@lists.r-forge.r-project.org > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel _______________________________________________ Rcpp-devel mailing list Rcpp-devel@lists.r-forge.r-project.org https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
