juniorRecommendation Systems
What is a user-item interaction matrix?
Updated May 16, 2026
Short answer
It is a matrix representing user interactions with items such as ratings or clicks.
Deep explanation
Rows represent users and columns represent items. Values represent explicit feedback (ratings) or implicit feedback (clicks, views). It is the foundation of collaborative filtering models.
Real-world example
Movie rating systems on IMDb.
Common mistakes
- Assuming matrix is always dense.
Follow-up questions
- What is sparsity?
- Explicit vs implicit feedback?