I've used them too, for years .. its my 'go-to' for sparse arrays on any internal/utility projects I'm using. I'm a bit hesitant to ship anything using them to end-users, though, due to the HP patent issue .. but thats just a gut feeling. Technically, there's not much out there that gives me the ease-of-use and performance of the Judy API for large, sparse or dense, datasets. I didn't find the API too challenging .. well, the fact is that once you get Judy integrated into your own datatype classes, its a dead cinch.

Sure would be nice to see Judy in modern architectures like Android/iOS, though ..