Prepare the rating matrix
Aggregate user-item interactions (ratings, purchases or implicit clicks) into a sparse matrix and split time-wise or by user for train/validation/test.
Factorise user-item interactions. Rank items by predicted preference.
Matrix factorisation learns low-rank latent vectors for users and items so that their dot-product predicts preferences. It is commonly used to produce ranked top-K recommendations, but care is needed for sparse data, cold-start items or users, popularity bias and hyperparameter selection.
Learning concept · Not a validated service
Matrix factorisation learns low-rank latent vectors for users and items so that their dot-product predicts preferences. It is commonly used to produce ranked top-K recommendations, but care is needed for sparse data, cold-start items or users, popularity bias and hyperparameter selection.
A proposed extension: personalise product lists for online shoppers by training a low-rank factorisation on historical purchase or rating data and serving top-K recommendations with a fallback for cold-start items.
Aggregate user-item interactions (ratings, purchases or implicit clicks) into a sparse matrix and split time-wise or by user for train/validation/test.
Fit a low-rank model (ALS or SGD for explicit/implicit feedback), tune latent dimension and regularisation on validation metrics.
Compute Precision@K, Recall@K and NDCG on held-out data and inspect per-user performance and popularity effects.
Expose a top-K API with caching, add item metadata fallbacks for cold-starts, and monitor coverage and drift.
The supplied starter builds a small user-item rating table from six users and five items, computes pairwise cosine similarity between users and uses the most similar user to recommend items that the target user has not seen. It implements a simple user-based nearest-neighbour recommender, not a matrix-factorisation algorithm with learned latent factors.
matrix = ratings.pivot_table(index="user", columns="item", values="rating").fillna(0)
user_similarity = pd.DataFrame(
cosine_similarity(matrix),
index=matrix.index,
columns=matrix.index,
)The code uses user-based cosine similarity on a tiny hard-coded rating table and does not implement matrix factorisation (ALS, SVD or learned latent vectors). It also lacks a realistic dataset split, ranking metrics (Precision@K/NDCG), and cold-start handling.
Proposed extension: replace the toy ratings with a real dataset (for example MovieLens), train a low-rank factorisation (ALS or SGD) for explicit/implicit feedback, tune with NDCG/Precision@K, and serve top-K results with metadata fallbacks.
This is a potential application pathway, not a delivered product. The supplied starter does not implement this service or validate it with real users.
Networkers Home runs this topic inside its AI Engineer Course, with placement support and hands-on labs.