Recommender systems are specialized models that make recommendations about how data points are connected within a dataset, without a clear distinction between training and testing data. They are based on the concept of interactions, which are the links between pairs of data points. Recommender systems are essential as an application of data science and are widely used today in various domains. This article will explore the various kinds of recommender systems and some useful recommendations about how you can go about building them.
First of all, the data recommender systems utilize consists of two main parts: the characteristic information (user data, keywords, categories, etc.) and user-item interactions data (e.g., review scores, number of likes, items bought, etc.). This data usually dwells in two different matrices, which constitute the recommender system's dataset. Note that these matrices can increase in size as new users or new items become available, something quite common in many recommender system scenarios.
There are various types of recommender systems, depending on how the data is used. There are collaborative filters (based on the interactions in the user-items data), content-based systems (employing the characteristic data), and combinations of the two, aka, hybrid models. These recommender systems types are useful, but each has its use cases, where it shines.
Yet, regardless of what systems are out there, you need to make sure you understand the data at hand before you start building your recommender system. After all, just because a particular kind of RS model works well for some problems, it doesn't mean it would work well with yours. That's why you need to examine your data closely and figure out what model is best suited for it. If, for example, you don't have enough user-item interaction data at your disposal, you may want to go for a content-based model, or perhaps a hybrid one. Also, if you need to add new items or new users to your dataset often, then maybe you should avoid collaborative filters altogether.
What's more, you may want to explore the deep learning option since deep neural networks (fully connected ones) handle this sort of problem. Of course, it's best to have lots of data for such a scenario for the DNNs to have a performance edge justifying the computation costs involved. So, it's good to consider other options, such as a simpler model for your recommender system. Also, note that the model you build has to be aligned with the project's requirements at hand.
However, it’s not just DNNs that require lots of data to work well. Collaborative filtering models are also in need of lots of information to work with to be useful. This data needs to be mainly in the interactions matrix; otherwise, the model won't work correctly, making more random recommendations. That's why data acquisition and data engineering are particularly crucial for recommender systems in general.
Beyond all these suggestions, you ought to have a good understanding of the functionality of recommender systems and the right mindset towards such problems. Additionally, you need to check the models after new data is added to the dataset, particularly new items. That's because these will take the form of empty columns in the user-item matrix, making the latter sparser and, therefore, the model less robust. However, there are ways around this issue, which stems from a good understanding of the recommender systems themselves.
If you wish to learn more about RS and the data science mindset in general, I invite you to check out my book Data Science Mindset, Methodologies, and Misconceptions. It’s been a few years now that it was published, but its content is still relevant and useful for any data scientist. So, check it out when you have the chance. Cheers!
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Zacharias Voulgaris, PhD
Passionate data scientist with a foxy approach to technology, particularly related to A.I.