I am attempting to cluster subgroups of substance abuser based on diagnostic status (nominal), age of onset (ordinal since it is binned in our set), etc. My question regards how to treat missing data for non-users. Obviously, these are subjects who will have no value for "age of onset" since they have no age where they started drinking (for example).
I was planning to use the Daisy package in R to calculate the Gower distance which would allow use of nominal and ordinal variables in distance computation. However, the ordinal variables like age of onset, number of days substances were used in the last week, and dosage of substance used by definition have missing values for non-users. We still need to treat non-users in a sensible way though, because one major prediction of this analysis is that clustering on the Gower distance will separate out one group of non-users and multiple subtypes of substance user.
If the question is not clear enough please let me know any additional information that might help.