VM-Rec: A Variational Mapping Approach for Cold-start User Recommendation

The cold-start problem is a common challenge for most recommender systems. With extremely limited interactions of cold-start users, conventional recommender models often struggle to generate embeddings with sufficient expressivity. Moreover, the absence of auxiliary content information of users exacerbates the presence of challenges, rendering most cold-start methods difficult to apply. To address this issue, our motivation is based on the observation that if a model can generate expressive embeddings for existing users with relatively more interactions, who were also initially cold-start users, then we can establish a mapping from few initial interactions to expressive embeddings, simulating the process of generating embeddings for cold-start users. Based on this motivation, we propose a Variational Mapping approach for cold-start user Recommendation (VM-Rec). Firstly, we generate a personalized mapping function for cold-start users based on their initial interactions, and parameters of the function are generated from a variational distribution. For the sake of interpretability and computational efficiency, we model the personalized mapping function as a sparse linear model, where each parameter indicates the association to a specific existing user. Consequently, we use this mapping function to map the embeddings of existing users to an embedding of the cold-start user in the same space. The resulting embedding has similar expressivity to that of existing users and can be directly integrated into a pre-trained recommender model to predict click through rates or ranking scores. We evaluate our method based on three widely used recommender models as pre-trained base recommender models, outperforming four popular cold-start methods on two datasets under the same base model.