Implementations of this interface define a notion of similarity between two users. Implementations should return values in the range -1.0 to 1.0, with 1.0 representing perfect similarity.
Returns the degree of similarity, of two users, based on the their preferences.
userID1first user ID
userID2second user ID
org.apache.mahout.cf.taste.common.TasteExceptionif an error occurs while accessing the data