Welcome to the lesson on preparing datasets for factorization machines. In this lesson, you will learn how to create a detailed dataset to be used in recommendation systems using factorization machines. Factorization machines are advanced models that capture complex interactions between different data features, making them powerful tools for making accurate recommendations.

Why focus on a structured dataset? A well-prepared dataset allows a factorization machine to learn meaningful relationships from the data, leading to better recommendation outcomes. This lesson will guide you through organizing your data in a format suitable for factorization machines.

Before diving into dataset preparation, let's briefly review how to read and understand our data files. You will work with three JSON files: tracks.json, users.json, and interactions.json. We already saw some examples of how tracks.json and users.json might look like. Let's take a look at the interactions.json file:

JSON
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1[
2  {
3    "user_id": 1,
4    "track_id": 1,
5    "rating": 3
6  },
7  {
8    "user_id": 1,
9    "track_id": 2,
10    "rating": 4
11  },
12... more data
13]

For each pair of a user and a track that this user interacted with, the file keeps track of the rating that the user gave to this track.

Here is a consolidated code snippet to load these files:

Python
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1import json
2
3# Reading JSON files
4with open('tracks.json', 'r') as tracks_file:
5    tracks = json.load(tracks_file)
6
7with open('users.json', 'r') as users_file:
8    users = json.load(users_file)
9
10with open('interactions.json', 'r') as interactions_file:
11    interactions = json.load(interactions_file)

This code reads the JSON files and prints their contents. Real-world data typically needs to be loaded like this before further processing.

The user-item interaction matrix is a fundamental component of many recommendation systems. It's a simplified way to understand which user interacts with which item and how.

Imagine you have three users and three tracks. Each interaction can be represented using dummy variables that indicate whether a user interacted with a track and what their rating was. For example:

In this table, 1 and 0 indicate the presence or absence of interaction between users and tracks. The rating column shows the rating a user gave to a track. This representation allows us to define user-item pairs. For example, the first row is for user1 and track1 pair, and it tells us that user1's rating for track1 is 3.

To make our dataset more informative, we incorporate auxiliary features such as user preferences and item statistics. These enrich the data, providing a better foundation for the system to learn from. Let's consider an example:

In the table, besides the user and track dummy variables and the rating column, we have additional auxiliary features:

• track_likes: Indicates the number of likes a track has received, providing a popularity measure. For example, the first row is for user1-track1 pair, so the track_likes in the first row is related to track1.
• user_listening_avg: Reflects the average listening duration for a user, which can indicate user engagement. Similarly, the first row is for user1-track1 pair, so the user_listening_avg in the first row is related to user1.
• genre_similarity: Measures the similarity between a user's genre preferences and a track's genre using cosine similarity. This feature captures the alignment between user tastes and item characteristics. Again, in the same manner, the first row is for user1-track1 pair, so the genre_similarity in the first row is related to the similarity between user1 and track1.

These features enrich the dataset, allowing factorization machines to capture deeper insights and nuances within the data.

Consider the genre encoding for tracks and computing a similarity index between user preferences and track genres. For example, encoding could look like:

Python
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1from sklearn.metrics.pairwise import cosine_similarity
2import numpy as np
3
4# Create genre encoding
5genre_encodings = {"Jazz": [1, 0, 0], "Pop": [0, 1, 0], "Rock": [0, 0, 1]}
6
7# Example: Calculating genre similarity
8user_genre_array = np.array([0.5, 0.8, 0.3])
9track_genre_array = np.array(genre_encodings["Jazz"])
10genre_similarity = cosine_similarity([user_genre_array], [track_genre_array])[0, 0]

Here, we encode genres and calculate genre similarity using cosine_similarity. This value reflects how closely user preferences match a track's genre, which can significantly influence recommendations.

In this part of the code, we create dummy variables for users and tracks. Dummy variables are binary indicators that represent whether a particular user or track is involved in the interaction.

Python
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1user_dummies = [1 if i == user_id else 0 for i in range(1, len(users) + 1)]
2track_dummies = [1 if i == track_id else 0 for i in range(1, len(tracks) + 1)]

• user_dummies: This list comprehension iterates over possible user indices. It assigns a 1 if the current index matches the user_id from the interaction, otherwise 0. This creates a binary representation for user involvement.
• track_dummies: Similarly, this creates a binary representation for track involvement by checking if the current index matches the track_id.

Next, we extract specific features from both user and track data using their respective IDs.

Python
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1user = next(user for user in users if user['id'] == user_id)
2track = next(track for track in tracks if track['id'] == track_id)
3
4track_likes = track['likes']
5user_listening_avg = user['time_listening_avg']

• We use the next() function to find the user and track objects that correspond to the current interaction's user and track IDs.
• track_likes is extracted to indicate the number of likes a track has.
• user_listening_avg is used to measure the average listening duration for a user.

This section calculates the genre similarity and consolidates all features into a single row.

Python
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1# Calculate genre similarity
2user_genre_array = np.array(list(user['genre_preferences'].values()))
3track_genre_array = np.array(genre_encodings[track['genre']])
4genre_similarity = cosine_similarity([user_genre_array], [track_genre_array])[0, 0]
5
6# Combine all features
7row = user_dummies + track_dummies + [track_likes, user_listening_avg, genre_similarity, rating]
8data.append(row)

• Genre similarity: This is calculated using cosine_similarity to measure how closely user preferences match a track's genre.
• Combining features: All dummy variables and features are consolidated into a single row, which is appended to the data list. This row contains user and track indicators, auxiliary features, and the interaction rating.

The final step is to gather all these elements into a structured data matrix.

Python
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1import pandas as pd
2
3# Prepare data
4data = []
5
6for interaction in interactions:
7    user_id = interaction['user_id']
8    track_id = interaction['track_id']
9    rating = interaction['rating']
10
11    # Create user and track dummy variables
12    user_dummies = [1 if i == user_id else 0 for i in range(1, len(users) + 1)]
13    track_dummies = [1 if i == track_id else 0 for i in range(1, len(tracks) + 1)]
14
15    # Extract user and track features
16    user = next(user for user in users if user['id'] == user_id)
17    track = next(track for track in tracks if track['id'] == track_id)
18
19    track_likes = track['likes']
20    user_listening_avg = user['time_listening_avg']
21
22    # Calculate genre similarity
23    user_genre_array = np.array(list(user['genre_preferences'].values()))
24    track_genre_array = np.array(genre_encodings[track['genre']])
25    genre_similarity = cosine_similarity([user_genre_array], [track_genre_array])[0, 0]
26
27    # Combine all features
28    row = user_dummies + track_dummies + [track_likes, user_listening_avg, genre_similarity, rating]
29    data.append(row)
30
31# Define column names
32columns = ['user1', 'user2', 'user3', 'track1', 'track2', 'track3', 
33           'track_likes', 'user_listening_avg', 'genre_similarity', 'rating']
34
35# Create DataFrame
36df = pd.DataFrame(data, columns=columns)

This complete code snippet constructs a comprehensive data frame with all the necessary data for factorization machines in recommendation systems.

Congratulations! You have learned how to prepare a dataset for factorization machines by creating a comprehensive data matrix. This matrix serves as the foundation for designing an effective recommendation system.

In this lesson, you revisited loading JSON files, learned to represent user-item interactions with dummy variables, and incorporated auxiliary features to enrich the data. Understanding these components is crucial for designing more accurate and personalized recommendation algorithms.

Now, it's time for you to apply these skills in the upcoming practice exercises. Your journey into creating sophisticated recommendation systems begins with mastering these foundations. Good luck, and remember to reference this lesson as needed!