The most basic user-based collaborative filtering can be implemented by initializing the previously described components, as follows:

First, load the data model:

StringItemIdFileDataModel model = new StringItemIdFileDataModel( 
    new File("/datasets/chap6/BX-Book-Ratings.csv", ";"); 

Next, define how to calculate how the users are correlated; for example, using the Pearson correlation:

UserSimilarity similarity =  
  new PearsonCorrelationSimilarity(model); 

Next, define how to tell which users are similar, that is, the users that are close to each other, according to their ratings:

UserNeighborhood neighborhood =  
  new ThresholdUserNeighborhood(0.1, similarity, model); 

Now, we can initialize a GenericUserBasedRecommender default engine with the data for model, neighborhood, and similar objects, as follows:

UserBasedRecommender recommender =  
new GenericUserBasedRecommender(model, neighborhood, similarity); 

That's it. Our first basic recommendation engine is ready. Let's discuss how to invoke recommendations. First, let's print the items that the user has already rated, along with ten recommendations for that user:

long userID = 80683; 
int noItems = 10; 
 
List<RecommendedItem> recommendations = recommender.recommend( 
  userID, noItems); 
 
System.out.println("Rated items by user:"); 
for(Preference preference : model.getPreferencesFromUser(userID)) { 
  // convert long itemID back to ISBN 
  String itemISBN = model.getItemIDAsString( 
  preference.getItemID()); 
  System.out.println("Item: " + books.get(itemISBN) +  
    " | Item id: " + itemISBN +  
    " | Value: " + preference.getValue()); 
} 
 
System.out.println("
Recommended items:"); 
for (RecommendedItem item : recommendations) { 
  String itemISBN = model.getItemIDAsString(item.getItemID()); 
  System.out.println("Item: " + books.get(itemISBN) +  
    " | Item id: " + itemISBN +  
    " | Value: " + item.getValue()); 
} 

This will provide the following recommendations, along with their scores, as output:

    Rated items:
    Item: The Handmaid's Tale | Item id: 0395404258 | Value: 0.0
    Item: Get Clark Smart : The Ultimate Guide for the Savvy Consumer | Item id: 1563526298 | Value: 9.0
    Item: Plum Island | Item id: 0446605409 | Value: 0.0
    Item: Blessings | Item id: 0440206529 | Value: 0.0
    Item: Edgar Cayce on the Akashic Records: The Book of Life | Item id: 0876044011 | Value: 0.0
    Item: Winter Moon | Item id: 0345386108 | Value: 6.0
    Item: Sarah Bishop | Item id: 059032120X | Value: 0.0
    Item: Case of Lucy Bending | Item id: 0425060772 | Value: 0.0
    Item: A Desert of Pure Feeling (Vintage Contemporaries) | Item id: 0679752714 | Value: 0.0
    Item: White Abacus | Item id: 0380796155 | Value: 5.0
    Item: The Land of Laughs : A Novel | Item id: 0312873115 | Value: 0.0
    Item: Nobody's Son | Item id: 0152022597 | Value: 0.0
    Item: Mirror Image | Item id: 0446353957 | Value: 0.0
    Item: All I Really Need to Know | Item id: 080410526X | Value: 0.0
    Item: Dreamcatcher | Item id: 0743211383 | Value: 7.0
    Item: Perplexing Lateral Thinking Puzzles: Scholastic Edition | Item id: 0806917695 | Value: 5.0
    Item: Obsidian Butterfly | Item id: 0441007813 | Value: 0.0
    
    Recommended items:
    Item: Keeper of the Heart | Item id: 0380774933 | Value: 10.0
    Item: Bleachers | Item id: 0385511612 | Value: 10.0
    Item: Salem's Lot | Item id: 0451125452 | Value: 10.0
    Item: The Girl Who Loved Tom Gordon | Item id: 0671042858 | Value: 10.0
    Item: Mind Prey | Item id: 0425152898 | Value: 10.0
    Item: It Came From The Far Side | Item id: 0836220730 | Value: 10.0
    Item: Faith of the Fallen (Sword of Truth, Book 6) | Item id: 081257639X | Value: 10.0
    Item: The Talisman | Item id: 0345444884 | Value: 9.86375
    Item: Hamlet | Item id: 067172262X | Value: 9.708363
    Item: Untamed | Item id: 0380769530 | Value: 9.708363