I want to use Spark's mllib.recommendation library to build a prototype recommender system. However, the format of the user data I have is something of the following format: AB123XY45678 CD234WZ12345 EF345OOO1234 GH456XY98765 .... If I want to use the mllib.recommendation library, according to the API of the Rating class, the user ids have to be integers (also have to be contiguous?) It looks like