On Tue, Jun 11, 2013 at 4:10 PM, Steve Jaffe <sja...@riskspan.com> wrote: > On Tuesday, June 11, 2013 3:02 PM, Romain Francois wrote: >> Maintaining the idea that this external pointer acts as a numeric vector >> without being one. >> >> What happens then you want its mean, its quantile or whatever. You >> essentially have to reimplement everything. >> >> So yes : can be done, but lots of work.
Agreed. > > I don't yet know enough about R internals to say, but in principle it seems > that if you have the subscript operator you'd be able to do practically any > statistical calculation. Without re-implementing anything. > > (One might also need elementwise addition, multiplication by scalars, etc -- > though in principle these can all be defined in terms of subscripting, I > assume that R has specialized versions of these for atomic vectors due to > performance. But in any case a relatively small number of fundamental > operations ought to be enough to make something "act like" a vector. And this > is exactly what Krzysztof provided the basics of.) > > When I say 'in principle' I'm thinking along the lines of C++ generics -- if > I have an object that overloads the subscript operator, then any >algorithm > that just uses subscripting will simply work. Whether that is true in R I'm > not certain, but what I think I know of the idea of >generics and > class-specific dispatch seems consistent with that picture. In case Dirk's reply wasn't clear on this point: almost all the basic functions which make R so pleasant for doing statistical analysis (mean/quantile/etc) use the vector at the C level and completely bypass the '[' function defined in R. In principle there's no reason you couldn't re-implement the relevant functions relying just on '[' and a few other basic functions but, as Romain points out, that's a lot of work and it would be slow. I think it's more useful to think of whether a limited subset of these operations will work for your application and whether you can convey the limits of the class to the user---I'd hate to convince a user that something _is_ a numeric vector and have them waste hours wondering why some piece of code is not working. Krzysztof _______________________________________________ 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
