I'm having a hard time understanding why people use any vector they find as a candidate for a recommender system.

In my mind, a recommender system requires a space where distance represents similarity. Of course, before you can construct such a space, first you need to settle on the type of distance you want to use (euclidean, angular, or anything else). Then you need a model (assuming we are talking about ML) to map your input (it could be an image, text, or anything else) to a point in that space. One major aspect of this model is that it's aware of the type of distance we've defined. If there's no notion of the distance in the model, definitely the output of the model is not going to have the attribute of "distance means similarity".

I'm asking this question because I've seen people use any vector they find to construct a recommender system. Here's an example of using a VAE's latent vectors for recommender systems:


I've also seen people using fastText word embeddings in the same way. I understand that all these embeddings/latent vectors form clusters in their spaces with some interesting patterns. But I don't think this is enough to assume the "distance represents similarity" requirement for a recommender system.

Please let me know if I'm missing anything here.

  • $\begingroup$ I think the training process forces the vectors that do the best job to emerge. Posting this as a comment, as "it works because it works" doesn't feel like the answer you were after :-) $\endgroup$ – Darren Cook Feb 15 at 21:21
  • $\begingroup$ @DarrenCook But the question is "does it really work?" or they are just assuming that it does? $\endgroup$ – Mehran Feb 20 at 15:55
  • $\begingroup$ It is trivial to make word embeddings, and reproduce results; or simply use a freely available pre-trained model. Contextual embeddings (like BERT) beat simple word embeddings (wordvec, fasttext, etc.) beat the algorithms that came before, in just about all NLP tasks. They are not perfect, but that is what I meant by "it works". $\endgroup$ – Darren Cook Feb 20 at 16:48

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