I guess I really should have described the data set better. Every level of that tree is fully populated. I can't have a separate table of buildings, because those buildings are specific to the given location. In database terms, both the location and the building name are in the primary key. (I do have a separate table of buildings, but that's in a separate data structure and describes the features they have in common.) I guess "cost" was a bad example to use, since it's unclear why it would vary by location. My bad.

I guess what I'm saying is that I periodically run across cases where the data is fundamentally deeply nested, and I need to start over from a fairly high level frequently (so I can't just grab the nested hash out and pass it into the other functions, avoiding long lookup chains.) Admittedly, it's not a frequent occurrence, but configuration files and simulations seem to be typical examples.