CS210 - Homework Assignment 1 - Movie Recommendation System - Solved

Data Input 
•      Ratings file: A text file that contains movie ratings. Each line has the name (with year) of a movie, its rating (range 0-5 inclusive), and the id of the user who rated the movie. A movie can have multiple ratings from different users. A user can rate a particular movie only once. A user can however rate

multiple movies. Here's a sample ratings file             Download sample ratings file  

•      Movies file: A text file that contains the genres of movies. Each line has a genre, a movie id, and the name (with year) of the movie. To keep it simple, each movie belongs to a single genre. Here's a sample movies file  Download sample movies file  

You may assume that input files will be correctly formatted, and data types will be as expected. So you don't need to write code to catch any formatting or data typing errors.

  

Task 1: Reading Data 
1.    [10 pts] Write a function read_ratings_data(f) that takes in a ratings file, and returns a dictionary. The dictionary should have movie as key, and the corresponding list of ratings as value.

For example:   movie_ratings_dict = { "The Lion King (2019)" : [6.0, 

7.5, 5.1], "Titanic (1997)": [7] }

2.    [10 pts] Write a function read_movie_genre(f) that takes in a movies file and returns a dictionary. The dictionary should have a one-to-one mapping between movie and genre.

For example   { "Toy Story (1995)" : "Adventure", "Golden Eye (1995)" : "Action" }

Watch out for unwanted leading and trailing whitespaces in movie and genre, remove them when encountered.

  

Task 2: Processing Data 
1.    [8 pts] Genre dictionary

Write a function create_genre_dict that takes as a parameter a movie-togenre dictionary, of the kind created in Task 1.2. The function should return another dictionary in which a genre is mapped to all the movies in that genre.

For example:   { genre1: [ m1, m2, m3], genre2: [m6, m7] }

2.    [8 pts] Average Rating

Write a function calculate_average_rating that takes as a parameter a ratings dictionary, of the kind created in Task 1.1. It should return a dictionary where the movie is mapped to its average rating computed from the ratings list.

For example:   {"Spider-Man (2002)": [3,2,4,5]}  ==>   {"Spider-Man (2002)": 3.5}

  

Task 3: Recommendation 
1.    [10 pts] Popularity based

In services such as Netflix and Spotify, you often see recommendations with the heading “Popular movies” or “Trending top 10”.

Write a function get_popular_movies that takes as parameters a dictionary of movie-to-average rating ( as created in Task 2.2), and an integer n (default should be 10). The function should return a dictionary ( movie:average rating, same structure as input dictionary) of top n movies based on the average ratings. (If there are fewer movies than n, it should all return all movies in order of top average ratings.)

2.    [8 pts] Threshold Rating

Write a function filter_movies that takes as parameters a dictionary of movieto-average rating (same as for the popularity based function above), and a threshold rating with default value of 3. The function should filter movies based on the threshold rating, and return a dictionary with same structure as the input. For example, if the threshold rating is 3.5, the returned dictionary should have only those movies from the input whose average rating is equal to or greater than 3.5.

3.    [12 pts] Popularity + Genre based

In most recommendation systems, genre of the movie/song/book plays an important role. Often features like popularity, genre, artist are combined to present recommendations to a user.

Write a function get_popular_in_genre that, given a genre, a genre-to-movies dictionary (as created in Task 2.1), a dictionary of movie:average rating (as created in Task 2.2), and an integer n (default 5), returns the top n most popular movies in that genre based on the average ratings. The return value should be a dictionary of movie-to-average rating of movies that make the cut. Genre categories will be from those in the movie:genre dictionary created in Task 1.2. Your code should handle the case when there are fewer than n movies in the data, as in Task 3.1 above.

4.    [8 pts] Genre Rating

One important analysis for the content platforms is to determine ratings by genre.

Write a function get_genre_rating that takes the same parameters as get_popular_in_genre above, except for n, and returns the average rating of the movies in the given genre.

5.    [12 pts] Genre Popularity

Write a function genre_popularity that takes as parameters a genre-to-movies dictionary (as created in Task 2.1), a movie-to-average rating dictionary (as created in Task 2.2), and n (default 5), and returns the top-n rated genres as a dictionary of genre:average rating. Hint: Use the above get_genre_rating function as a helper.

  

Task 4 (User Focused) 
1.    [10 pts] Read the ratings file to return a user-to-movies dictionary that maps user ID to the associated movies and the corresponding ratings. Write a function named read_user_ratings for this, with the ratings file as the parameter.

For example: { u1: [ (m1, r1), (m2, r2) ], u2: [ (m3, r3), (m8, r8) ] 

} where ui is user ID, mi is movie, ri is corresponding rating.

2.    [12 pts] Write a function get_user_genre that takes as parameters a user id, the user-to-movies dictionary (as created in Task 4.1 above), and the movieto-genre dictionary (as created in Task 1.2), and returns the top genre that the user likes based on the user's ratings.

Here, the top genre for the user will be determined by taking the average rating of the movies genre-wise that the user has rated.

3.    [12 pts] Recommend 3 most popular (highest average rating) movies from the user's top genre that the user has not yet rated. Write a function recommend_movies for this, that takes a parameters a user id, the user-to-movies dictionary (as created in Task 4.1 above), the movie-to-genre dictionary (as created in Task 1.2), and the movie-to-average rating dictionary (as created in Task 2.2). The function should return a dictionary of movie-toaverage rating. (Return all if fewer than 3 movies make the cut.)