notebook.community

Collaborative Filtering

User-based Nearest Neighbor

Find other users who are similar to the test case (person of interest)

$$Pred(i) = \bar{r}_u+\frac{\sum_{n\in neighbors(u)} similarity(u,n).(r_{ni} - \bar{r}_{n})}{\sum_{n\in neighbors(u)} similarity(u,n)}$$

$\bar{r}_u$: average rating of user $u$

Item-based Nearest Neighbor

Find similar items

$$Pred() = \frac{\sum_{j\in ratedItems(u)} similarity(i,j).r_{uj}}{\sum_{j\in ratedItems(u)} similarity(i,j)}$$

Latent Factor (Matrix Factorization)

Rating matrix $A_{users \times items}$
User feature matrix $U_{users \times features}$
Item feature matrix $M_{items \times features}$
Predicted matrix: $U\times M^T$



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