www.cs.amherst/~ccm/cs111/prog4.html

Fourth Programming Assignment

Your assignment is to write a program to implement a recommender system like you find on Netflix or Amazon: ``people who liked that movie also enjoyed X.'' Your program makes use of two text files that I will provide, called books.txt and ratings.txt

• books.txt contains a list of book titles and authors, one book per line, like this:

  Douglas Adams,The Hitchiker's Guide To The Galaxy
  Richard Adams,Watership Down
  Mitch Albom,The Five People You Meet in Heaven
  Laurie Halse Anderson,Speak
  Maya Angelou,I Know Why the Caged Bird Sings
  Ann Brashares,The Sisterhood of the Travelling Pants 
  ... 
  

  and so forth. Notice that the author name is separted from the book title by a comma. This file will contain 35 titles.

• ratings.txt contains user's ratings of these books. Each rating occupies two lines: the first has the person's userid, and the second has 35 integers (matching the number of books) with values between -3 (hated it) and +3 (loved it). If the person has not read the book the rating is 0. The integers are separated by spaces. Like this:

  jeffAmherst
  0 0 1  -3  1  1 3 -3 2 2 -3 3 0 0 0 1 1 -1 -3 0 0 3 1 -2 -3  1 -2 -2 2 2 0 0 0 0 0 
  ephriam
  0 0 0 0 0 -3 0 0 0 0 0 0 0 0 0 0 0 0 0 -3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 
  cap99
  3 3 3 3 3  -3 -3 -3 -3 0 0 0 0 0 0 0 0 0  -3 3 -3 3 -3 3 3 3 3 3 -3 -3 -3 -3 -3 
  ...
  

  And so forth. This file will contain between 10 and 100 user ratings, to be determined later.

  From this data we learn, for example, that user jeffAmherst didn't read the first two books on the list. He liked (a little bit) the book by Mitch Albom, and hated the book by Laurie Halse Anderson. We also see that ephriam read only two books and didn't like either of them, and that cap99 has strong opinions (love or hate) about the books she reads.

What your program does

1. Open the books.txt file and read the names and titles into an appropriate data structure.

2. Open the ratings.txt file and reads the ratings data into an appropriate data structure.

3. Offer the user a menu of options for how to use the data, including:
   • Show titles. The program prints all the book titles in its database.
   • See ratings. The user enters a book title and the program displays how many users have read it, how many gave it a postive score, and how many gave it a negative score. (If you like, report more detailed information, such as the number of strong and weak scores, or the average score.)
   • Rate a book. The user enters his or her userid, and a book title, and then a rating (between -3 and +3). The program updates the user rating for that book.
   • Make a recommendation. The user enters a book title; the program responds with ``People who liked this book also liked'' ... and a list of titles. To build this list, the program must go through the ratings and find every user who gave the title a positive score; then it records other books that received positive scores from this user. Ideally your program prints a list of unique titles (no duplicates).
   • Done. The user is finished. The (possibly updated) ratings data is written to ratings.txt (thus over-writing the old data). The files are closed and the program stops.

4. The program should repeat the above process of printing a menu and inviting the user to choose an option (different user ids are allowed), continuing until the user is done. Invent a convenient way for the user to specify which action to take each time.

5. Advice. This assignment is mostly about choosing appropriate data structures to hold the data. Your choices include strings, lists, tuples, dictionaries, and sets. There is not a perfect answer here, but your choice will affect how easy it is to accomplish certain tasks, so think carefully about the implications before you make your decision. It is perfectly reasonable to use more than one data structure to make the program easier to write.

6. More advice. Proceed step-by-step and add one option at a time. You can get substantial partial credit if, say, just 4 of 5 options are offered, but they work perfectly. This is a better strategy than turning in a program that offers options that don't work right.

7. More advice. Save a backup copy of books.txt and ratings.txt, in case your program accidentally messes them up while you are figuring out how to use Python for files.

Turning It In

1. Name your file recommend.py.
2. Make a trace file showing how the menu options work. Choose options in this order:
   • Show titles
   • See ratings. Choose the third title in the list.
   • Recommend. Choose the third title in the list.
   • Rate a book. Choose the third title and the third user. Give this book a new rating of -3
   • See ratings. Re-run this with the third title to show the update.
   • Recommend. Re-run this with the third title to show the update.
   • (Additional commands to show off any robustness features that you have added.)
   • Done