engine for discrim

[topepo]

For the naive Bayes engine, I would add a condition inside of .onLoad:

if (any(loadedNamespaces() == "discrim")) {
   add_naive_Bayes_h2o()
}

I can put a note in the discrim docs that, if they want the h2o engine, they should load discrim and then this package.

[stevenpawley]

Thanks!