  We introduce a new version of forward stepwise regression. Our modification
finds solutions to regression problems where the selected predictors appear in
a structured pattern, with respect to a predefined distance measure over the
candidate predictors. Our method is motivated by the problem of predicting
HIV-1 drug resistance from protein sequences. We find that our method improves
the interpretability of drug resistance while producing comparable predictive
accuracy to standard methods. We also demonstrate our method in a simulation
study and present some theoretical results and connections.
