Machine Learning in Java - Second Edition

In-memory databases

Last, but not least, the data model can be created on the fly and held in memory. A database can be created from an array of preferences, which will hold user ratings for a set of items.

We can proceed as follows. First, we create a FastByIdMap hash map of preference arrays, PreferenceArray, which stores an array of preferences:

FastByIDMap <PreferenceArray> preferences = new FastByIDMap    <PreferenceArray> ();  

Next, we can create a new preference array for a user that will hold their ratings. The array must be initialized with a size parameter that reserves that many slots in the memory:

PreferenceArray prefsForUser1 =  
  new GenericUserPreferenceArray (10);   

Next, we set the user ID for the current preference at the position ...