# Speeding up Memory-based Collaborative Filtering with Landmarks

## TL;DR

This paper introduces a landmark-based method to significantly reduce the computational cost of memory-based collaborative filtering, improving efficiency while maintaining recommendation quality.

## Contribution

The authors propose a landmark-based approach to efficiently compute user similarities, addressing the scalability issue in memory-based CF algorithms.

## Key findings

- Outperforms eight CF algorithms in computational efficiency
- Consistently outperforms existing methods on two different datasets
- Reduces similarity computation complexity significantly

## Abstract

Recommender systems play an important role in many scenarios where users are overwhelmed with too many choices to make. In this context, Collaborative Filtering (CF) arises by providing a simple and widely used approach for personalized recommendation. Memory-based CF algorithms mostly rely on similarities between pairs of users or items, which are posteriorly employed in classifiers like k-Nearest Neighbor (kNN) to generalize for unknown ratings. A major issue regarding this approach is to build the similarity matrix. Depending on the dimensionality of the rating matrix, the similarity computations may become computationally intractable. To overcome this issue, we propose to represent users by their distances to preselected users, namely landmarks. This procedure allows to drastically reduce the computational cost associated with the similarity matrix. We evaluated our proposal on two distinct distinguishing databases, and the results showed our method has consistently and considerably outperformed eight CF algorithms (including both memory-based and model-based) in terms of computational performance.