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Metadata Embeddings for User and Item Cold-start Recommendations

F401afbfb8100568304f0caf45c79575?s=47 Maciej Kula
September 20, 2015

Metadata Embeddings for User and Item Cold-start Recommendations


Maciej Kula

September 20, 2015


  1. Metadata Embeddings for User and Item Cold-start Recommendations September, 2015

  2. Hi, I’m Maciej Kula @maciej_kula

  3. We collect the world of
 fashion into a customisable

  4. 480 retailers 4 12,000 designers 12,000 new products added 

    every day. We continually scrape fashion products from around the web:
  5. Most recent items 
 are the most relevant. Traditional MF

    will not do, 
 need a hybrid model. Products are 
 relatively short-lived. A huge cold-start problem. Made worse by characteristics of fashion. 5
  6. 6 A new model, called LightFM. 6

  7. 7 Users and items characterised by sets of metadata features:

    • Designer • Category • Colour • User Country • User Gender • Interaction Context (desktop/mobile)
  8. • Each feature represented by a latent vector. • The

    representation for an item or a user is the elementwise sum of the representation of their features. • Predictions are given by the dot product of the user and item representations. 8 8
  9. 9 Let 1. FU be the (no. users x no.

    user features) user feature matrix 2. FI be the (no. items x no. item features) item feature matrix 3. EU be the (no. user features x latent dimensionality) user feature embedding matrix 4. EI be the (no. item features x latent dimensionality) item feature embedding matrix Then the user-item matrix can be expressed as FU EU (FI EI )T FU and FI are given and we estimate EU and EI .
  10. 10 If we only use item/user indicator variables as features

 (FU and FI are identity matrices), the model reduces to a traditional MF model. As we add metadata features,we gain the ability to make predictions for cold start items and users.
  11. 11 Experiments on two datasets MovieLens 10M 
 10 million

    rankings, 71 thousand users, 
 10 thousand movies. CrossValidated 
 6 thousand users, 44 thousand questions, 
 190 thousand answers and comments. Full experiment code available at
  12. 12 Training data: • In the Movielens experiment, items rated

    4 or higher are positives. • In the CrossValidated dataset, answered questions are positives 
 and negatives are randomly sample unanswered questions. Two experiments: • warm-start: random 80%/20% split of all interactions. • cold-start: all interactions for 20% of items are moved to the test set. 12
  13. 13 MF: a conventional matrix factorisation model. LSI-LR: a content-based

    model using per-user logistic regression models on top of principal components of the item metadata matrix. LSI-UP: a hybrid model that represents user profiles as linear combinations of items' content vectors, then applies LSI to the resulting matrix to obtain latent user and item representations. Baselines
  14. 14 Results LightFM performs as well as or better than

    standard MF in the warm-start setting. It outperforms the content-based baselines 
 in the cold-start setting. We can have a single model that performs
 well across the data sparsity spectrum.
  15. 15 Warm Cold Warm Cold LSI-LR 0.662 0.660 0.686 0.690

    LSI-UP 0.636 0.637 0.687 0.681 MF 0.541 0.508 0.762 0.500 LightFM (tags) 0.675 0.675 0.744 0.707 LightFM (tags + ids) 0.682 0.674 0.763 0.716 LightFM (tags + about) 0.695 0.696 CrossValidated MovieLens
  16. 16 Example with our own data Small sample of product

    page views. Very sparse. Mixture of warm and cold-start users and items. Item implicit binary feedback setting. Model trained with WARP loss.
  17. 17 Metadata features help • 0.59 AUC with no metadata

    (standard MF) • 0.91 with both item and user features
  18. 18 Metadata representations useful in their own right. 18

  19. 19 `regression' `least squares', `multiple regression' `MCMC' `BUGS', `Metropolis-Hastings', `Beta-Binomial'

    `survival' `epidemiology', `Cox model' `art house' `pretentious', `boring', `graphic novel' `dystopia' `post-apocalyptic', `futuristic' `bond' `007', `secret service', `nuclear bomb' Tag similarity
  20. Categories similar to Suits 20 Ties Shirts Designers similar to

    Levi’s G-Star Raw Armani Jeans 20
  21. 21 Useful for • Explaining recommendations • Tag recommendations

  22. 22 We've open-sourced a Python implementation pip install lightfm

  23. 23 from lightfm import LightFM model = LightFM(no_components=30), user_features=user_features,

    item_features=item_features, epochs=20) 23
  24. 24 Multiple loss functions • Logistic loss for explicit binary

    feedback • BPR • WARP • k-th order statistic WARP loss
  25. Two learning rate schedules: • adagrad • adadelta Trained with

    asynchronous stochastic gradient descent. 25
  26. thank you