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Recommendation Systems 2 — Understanding User-Based Collaborative Filtering Techniques

Building Recommendation Systems — Part 2/20

Ayşe Kübra Kuyucu
DataDrivenInvestor
Published in
9 min readMar 18, 2025

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Table of Contents
1. The Basics of User-Based Collaborative Filtering
2. Calculating Similarity in User-Based Systems
2.1. Pearson Correlation Coefficient
2.2. Cosine Similarity
3. Advantages of User-Based Collaborative Filtering
4. Challenges and Solutions in User-Based Systems
4.1. Scalability Issues
4.2. Sparsity Problem
5. Implementing User-Based Collaborative Filtering
6. Case Studies: Success Stories of User-Based Systems

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1. The Basics of User-Based Collaborative Filtering

User-based collaborative filtering is a technique used in recommendation systems to predict the preferences of a user by collecting preferences from many users. The assumption is that those who agreed in the past will agree in the future about other items. Here’s how it fundamentally works:

First, the system gathers input about user preferences. This could be through explicit methods like ratings or implicit methods such as browsing history. Next, it identifies users with similar preferences, often called neighbors. The similarity between users is calculated using various statistical techniques, which we will explore in more detail in subsequent sections.

The final step involves generating recommendations. Once similar users are identified, the system predicts the current user’s interest based on the preferences of these similar users. For instance, if user A likes items 1, 2, and 3, and user B likes items 2, 3, and 4, and they are determined to be similar, then the system might recommend item 4 to user A.

This method leverages user similarities to enhance the accuracy of the recommendations provided. By focusing on the collective…

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