Now the model uses sparse Mahout matrices instead of HashMaps of Mahout Vectors. Additionally, I've changed context awareness logic. Context vectors now should be derived when a user and item are given. Please see ContextDeriver to see what interface you should implement for the appropriate logic. This became flexible and more compatible to the Mahout API, but requires library users to implement their own Context derivation logic. I am going to add an example soon. As soon as the new structure is unit tested, and evaluated against previous examples, I will merge this to the trunk branch, and this will be tagged as a milestone.