1 // Main Part 2 about Movie Recommendations 

     2 // at Danube.co.uk

     3 //===========================================

     4 

     5 object M2 {

     6 

     7 import io.Source

     8 import scala.util._

     9 

    10 // (1) Implement the function get_csv_url which takes an url-string

    11 //     as argument and requests the corresponding file. The two urls

    12 //     of interest are ratings_url and movies_url, which correspond 

    13 //     to CSV-files.

    14 //

    15 //     The function should ReTurn the CSV-file appropriately broken

    16 //     up into lines, and the first line should be dropped (that is without

    17 //     the header of the CSV-file). The result is a list of strings (lines

    18 //     in the file).

    19 

    20 def get_csv_url(url: String) : List[String] = ???

    21 

    22 

    23 val ratings_url = """https://nms.kcl.ac.uk/christian.urban/ratings.csv"""

    24 val movies_url = """https://nms.kcl.ac.uk/christian.urban/movies.csv"""

    25 

    26 // testcases

    27 //-----------

    28 //:

    29 //val movies = get_csv_url(movies_url)

    30 

    31 //ratings.length  // 87313

    32 //movies.length   // 9742

    33 

    34 

    35 

    36 // (2) Implement two functions that process the CSV-files from (1). The ratings

    37 //     function filters out all ratings below 4 and ReTurns a list of 

    38 //     (userID, movieID) pairs. The movies function just ReTurns a list 

    39 //     of (movieID, title) pairs. Note the input to these functions, that is

    40 //     the argument lines, will be the output of the function get_csv_url.

    41 

    42 

    43 def process_ratings(lines: List[String]) : List[(String, String)] = ???

    44 

    45 def process_movies(lines: List[String]) : List[(String, String)] = ???

    46 

    47 

    48 // testcases

    49 //-----------

    50 //val good_ratings = process_ratings(ratings)

    51 //val movie_names = process_movies(movies)

    52 

    53 //good_ratings.length   //48580

    54 //movie_names.length    // 9742

    55 

    56 

    57 

    58 

    59 // (3) Implement a grouping function that calculates a Map

    60 //     containing the userIDs and all the corresponding recommendations 

    61 //     (list of movieIDs). This  should be implemented in a tail

    62 //     recursive fashion, using a Map m as accumulator. This Map m

    63 //     is set to Map() at the beginning of the calculation.

    64 

    65 def groupById(ratings: List[(String, String)], 

    66               m: Map[String, List[String]]) : Map[String, List[String]] = ???

    67 

    68 

    69 // testcases

    70 //-----------

    71 //val ratings_map = groupById(good_ratings, Map())

    72 //val movies_map = movie_names.toMap

    73 

    74 //ratings_map.get("414").get.map(movies_map.get(_)) 

    75 //    => most prolific recommender with 1227 positive ratings

    76 

    77 //ratings_map.get("474").get.map(movies_map.get(_)) 

    78 //    => second-most prolific recommender with 787 positive ratings

    79 

    80 //ratings_map.get("214").get.map(movies_map.get(_)) 

    81 //    => least prolific recommender with only 1 positive rating

    82 

    83 

    84 

    85 // (4) Implement a function that takes a ratings map and a movie_name as argument.

    86 //     The function calculates all suggestions containing

    87 //     the movie in its recommendations. It ReTurns a list of all these

    88 //     recommendations (each of them is a list and needs to have the movie deleted, 

    89 //     otherwise it might happen we recommend the same movie).

    90 

    91 

    92 def favourites(m: Map[String, List[String]], mov: String) : List[List[String]] = ???

    93 

    94 

    95 // testcases

    96 //-----------

    97 // movie ID "912" -> Casablanca (1942)

    98 //          "858" -> Godfather

    99 //          "260" -> Star Wars: Episode IV - A New Hope (1977)

   100 

   101 //favourites(ratings_map, "912").length  // => 80

   102 

   103 // That means there are 80 users that recommend the movie with ID 912.

   104 // Of these 80  users, 55 gave a good rating to movie 858 and

   105 // 52 a good rating to movies 260, 318, 593.

   106 

   107 

   108 

   109 // (5) Implement a suggestions function which takes a rating

   110 //     map and a movie_name as arguments. It calculates all the recommended

   111 //     movies sorted according to the most frequently suggested movie(s) first.

   112 

   113 def suggestions(recs: Map[String, List[String]], 

   114                 mov_name: String) : List[String] = ???

   115 

   116 

   117 // testcases

   118 //-----------

   119 

   120 //suggestions(ratings_map, "912")

   121 //suggestions(ratings_map, "912").length  

   122 // => 4110 suggestions with List(858, 260, 318, 593, ...)

   123 //    being the most frequently suggested movies

   124 

   125 

   126 

   127 // (6) Implement a recommendations function which generates at most

   128 //     *two* of the most frequently suggested movies. It ReTurns the 

   129 //     actual movie names, not the movieIDs.

   130 

   131 

   132 def recommendations(recs: Map[String, List[String]],

   133                     movs: Map[String, String],

   134                     mov_name: String) : List[String] = ???

   135 

   136 

   137 

   138 // testcases

   139 //-----------

   140 // recommendations(ratings_map, movies_map, "912")

   141 //   => List(Godfather, Star Wars: Episode IV - A NewHope (1977))

   142 

   143 //recommendations(ratings_map, movies_map, "260")

   144 //   => List(Star Wars: Episode V - The Empire Strikes Back (1980), 

   145 //           Star Wars: Episode VI - Return of the Jedi (1983))

   146 

   147 // recommendations(ratings_map, movies_map, "2")

   148 //   => List(Lion King, Jurassic Park (1993))

   149 

   150 // recommendations(ratings_map, movies_map, "0")

   151 //   => Nil

   152 

   153 // recommendations(ratings_map, movies_map, "1")

   154 //   => List(Shawshank Redemption, Forrest Gump (1994))

   155 

   156 // recommendations(ratings_map, movies_map, "4")

   157 //   => Nil  (there are three ratings for this movie in ratings.csv but they are not positive)     

   158 

   159 

   160 

   161 }