Recsys - Embeddings

• Overview
• Comparative Analysis of Different Methods
• Factorization Machines v/s Matrix Factorization
• Demographics
• Content-Based Filtering

Overview

• This article will go over different methods of generating embeddings in recommender systems.

1. Neural Collaborative Filtering (NCF):
   • Input: NCF takes user-item interaction data as input, typically in the form of a user-item interaction matrix or a set of user-item pairs.
   • Computation: NCF employs neural networks, such as multi-layer perceptrons (MLPs) or convolutional neural networks (CNNs), to model the user-item interactions. It learns the latent representations (embeddings) of users and items by training the neural network using backpropagation and optimization techniques.
   • Output: The output of NCF is the learned embeddings of users and items, which are dense vectors in an embedding space. These embeddings capture the latent features and preferences of users and items.
   • Retrieval: After generating the embeddings, recommendations can be made by computing similarity or affinity scores between user and item embeddings. The most similar or highest-scoring items can be retrieved as recommendations for a given user.
   • The Neural Collaborative Filtering (NCF) model is a neural network-based approach for collaborative filtering, which aims to make personalized recommendations by analyzing user-item interactions. NCF offers a unique perspective on matrix factorization by incorporating non-linearities into the model. In TensorFlow, the NCF implementation takes a sequence of (user ID, item ID) pairs as input.
   • The NCF model consists of two main components: matrix factorization and a multilayer perceptron (MLP) network. The input pairs are split and fed separately into these components.
     1. Matrix Factorization:
        • In this step, embeddings representing users and items are learned through matrix factorization.
        • The embeddings are obtained by multiplying user and item representations.
     2. Multilayer Perceptron (MLP) Network:
        • The input pairs are also passed through an MLP network.
        • The MLP network comprises multiple hidden layers with non-linear activation functions.
        • This network captures complex patterns and interactions between users and items.
   • The outputs from both the matrix factorization and MLP network are then combined and fed into a single dense layer. This final layer predicts the likelihood of a given user interacting with a specific item.
   • By combining the strengths of matrix factorization and deep learning techniques, NCF provides an effective approach for collaborative filtering, enabling personalized recommendations based on user-item interactions.
2. Matrix Factorization (MF):
   • Input: MF takes the user-item interaction matrix as input, where rows represent users, columns represent items, and the entries indicate the interactions or ratings.
   • Computation: MF factorizes the user-item interaction matrix into two low-rank matrices: one representing user embeddings and the other representing item embeddings. The factorization is typically done using optimization techniques like Singular Value Decomposition (SVD) or Alternating Least Squares (ALS).
   • Output: The output of MF is the learned embeddings of users and items, represented as latent vectors in an embedding space. These embeddings capture the latent features and preferences of users and items.
   • Retrieval: Recommendations are made by computing similarity scores between user and item embeddings. Items with the highest similarity scores to a given user can be retrieved as recommendations.
3. Factorization Machines (FM):
   • Input: FM takes user and item features as input, along with the user-item interaction data.
   • Computation: FM models the interactions between user and item features by factorizing the feature interactions using matrix factorization techniques. It learns the latent representations of users and items by considering both linear and non-linear feature interactions.
   • Output: The output of FM is the learned embeddings of users and items, capturing their latent features and preferences.
   • Retrieval: Similar to other methods, recommendations are made by computing similarity scores between user and item embeddings. The most similar items to a given user can be retrieved as recommendations.
4. Deep Matrix Factorization (DMF):
   • Input: DMF takes user and item features, along with user-item interaction data, as input.
   • Computation: DMF combines matrix factorization with deep neural networks. It utilizes the low-rank matrix factorization to capture linear relationships and incorporates deep neural networks to model non-linear interactions between users and items.
   • Output: The output of DMF is the learned embeddings of users and items, which capture their latent features and preferences.
   • Retrieval: Recommendations are made by computing similarity scores between user and item embeddings, followed by retrieving the most similar items for a given user.
5. Graph Neural Networks (GNN):
   • Input: GNN takes user-item interaction graph data as input, where users and items are represented as nodes, and interactions as edges.
   • Computation: GNNs propagate information through the user-item interaction graph to learn node embeddings. They capture the relational dependencies and interactions among users, items, and their connections in the graph.
   • Output: The output of GNN is the learned embeddings of users and items, capturing their characteristics and preferences in the graph structure.
   • Retrieval: After generating the embeddings, recommendations can be made by computing similarity scores or applying graph-based algorithms to find the most relevant items for a given user. The recommendations are typically based on the similarity or affinity between user and item embeddings. - In summary, each method involves different computations and techniques to generate embeddings. The input varies from user-item interaction data to user-item feature data or graph-based data. The output is the learned embeddings, which capture the latent features and preferences of users and items. After obtaining the embeddings, recommendations are made by computing similarity or applying graph-based algorithms to retrieve the most relevant items for users.

Comparative Analysis of Different Methods

• Here’s a table summarizing the different methods and their characteristics to help you decide which approach to choose for your recommendation system:

• The choice of method depends on various factors, including the specific requirements of your recommendation system and the characteristics of your data. Here are some considerations:

  • Complexity of Data: If your data exhibits complex patterns and interactions, methods like NCF and DMF that leverage deep learning techniques may be suitable.

  • Data Sparsity: For sparse data, where users have limited interactions with items, methods like FM that handle high-dimensional and sparse data well may be beneficial.

  • Interpretability: If interpretability is important, methods like MF offer simplicity and ease of understanding due to their matrix factorization approach.

  • Graph Structure: If your recommendation system involves graph-based data, such as user-item interaction graphs, GNNs can capture relational dependencies and perform well in such scenarios.

  • Data Availability: NCF and DMF typically require a significant amount of training data, while methods like FM can handle smaller datasets effectively.

Factorization Machines v/s Matrix Factorization

• Factorization Machines (FM) and Matrix Factorization (MF) are both techniques used in recommender systems, but they differ in their approach and modeling capabilities. Here are the key differences between FM and MF:

1. Modeling Approach:
   • MF: Matrix Factorization is a traditional approach that directly factorizes the user-item interaction matrix. It decomposes the matrix into two low-rank matrices representing user and item embeddings.
   • FM: Factorization Machines, on the other hand, are a more general approach that can handle not only user-item interactions but also feature interactions. FM models the interactions between user and item features, capturing both linear and non-linear dependencies.
2. Handling Feature Interactions:
   • MF: Matrix Factorization primarily focuses on capturing the interactions between users and items based on their ratings or interactions. It does not explicitly model the feature interactions.
   • FM: Factorization Machines are designed to model feature interactions, making them more flexible in capturing complex relationships between features. FM factorizes the feature interactions to learn latent representations and capture higher-order dependencies.
3. Data Representation:
   • MF: Matrix Factorization typically operates on a user-item interaction matrix, where rows represent users, columns represent items, and the matrix entries correspond to interactions or ratings.
   • FM: Factorization Machines take user and item features as input, along with the user-item interaction data. They explicitly consider the feature vectors associated with users and items.
4. Model Flexibility:
   • MF: Matrix Factorization provides a simpler and more interpretable model, as it directly decomposes the user-item interaction matrix. However, it has limited modeling capabilities for capturing non-linear relationships and feature interactions.
   • FM: Factorization Machines offer more flexibility in modeling complex relationships by capturing both linear and non-linear feature interactions. They can handle high-dimensional and sparse data more effectively than MF.
5. Application Scope:
   • MF: Matrix Factorization is commonly used in collaborative filtering-based recommender systems, where the focus is on user-item interactions and predicting ratings or preferences.
   • FM: Factorization Machines have a wider range of applications beyond collaborative filtering. They can be used for recommendation tasks that involve feature interactions, such as click-through rate prediction, ad targeting, and personalized marketing.

• In summary, while both MF and FM are used in recommender systems, MF primarily focuses on matrix factorization of user-item interactions, whereas FM is more versatile and captures both linear and non-linear feature interactions. FM provides more flexibility in modeling complex relationships, making it applicable to various recommendation tasks beyond traditional collaborative filtering.

Demographics

• When it comes to demographic filtering, one common approach is to create user embeddings based on demographic information. User embeddings capture the underlying characteristics and preferences of users, allowing for personalized recommendations. Here are a few options for generating user embeddings in the context of demographic filtering:

1. One-Hot Encoding:
   • One simple way to represent demographic information is through one-hot encoding. Each demographic attribute (e.g., age group, gender, location, occupation) is encoded as a binary vector, with a value of 1 indicating the presence of a particular attribute and 0 otherwise.
   • User embeddings can be created by concatenating or averaging the one-hot encoded vectors of the demographic attributes.
   • Although straightforward, one-hot encoding can result in high-dimensional and sparse representations.
2. Embedding Layers:
   • Another approach is to use embedding layers in neural networks to learn low-dimensional representations of the demographic attributes.
   • Each demographic attribute is mapped to an embedding space of lower dimensionality (e.g., 10-dimensional vector).
   • User embeddings are formed by concatenating or averaging the embeddings of the demographic attributes.
   • Embedding layers allow for capturing non-linear relationships between demographic attributes and can handle high-dimensional and sparse data more efficiently.
3. Pretrained Embeddings:
   • Pretrained embeddings, such as word embeddings (e.g., Word2Vec, GloVe), can also be used to represent demographic attributes.
   • Word embeddings trained on large text corpora often capture semantic relationships between words.
   • By assigning pretrained word embeddings to demographic attribute values, user embeddings can be formed by aggregating or averaging the embeddings of the corresponding attribute values.
4. Autoencoders:
   • Autoencoders are neural network architectures that aim to learn compressed representations of input data.
   • In the context of demographic filtering, autoencoders can be used to learn lower-dimensional representations of user demographic information.
   • User embeddings are generated by feeding the demographic attributes as input to the autoencoder and extracting the encoded representations from the bottleneck layer.

• These approaches provide different ways to represent and generate user embeddings based on demographic information. The choice of method depends on the specific characteristics of the demographic data, the complexity of relationships between attributes, and the availability of training data. It’s important to experiment with different techniques and evaluate their performance on recommendation tasks to determine the most suitable approach for your application.

Content-Based Filtering

• Content-based filtering recommends items to users based on the similarity between the items’ content and the user’s preferences. It relies on item features such as textual descriptions, attributes, or metadata.
• Techniques like TF-IDF (Term Frequency-Inverse Document Frequency) or word embeddings (e.g., Word2Vec, GloVe) can be used to represent item features. Recommendations are made by computing the similarity between the user’s preferences or profile and the item features, often using cosine similarity or other distance metrics.