Ensemble of Recommendation Algorithm

PySpark implementation of recommender ensemble (Bagging ensemble for now).

More details about the best practices for building recommendation systems can be found at Recommenders GitHub.

Prerequisite

• Basic knowledge on recommender systems
• pySpark

How It Works and Why

Bagging (Bootstrap aggregating) is a machine learning (ML) ensemble method designed to improve the stability and accuracy of ML algorithms used in statistical classification and regression.

One of the most successful application of Bagging is Random Forest.

The method implemented here uses the exact same approach as the conventional Bagging ensemble:

1. Train M recommender models (base models) with bootstrapping of a training set

2. To predict item ratings, generate M predictions by using the base models and then average the predicted ratings for each item

3. For recommending top k items, on the other hand, generate M recommendation lists of k items with the base models, combine the list.

Currently, this repo implements three combining methods average, sum, and count.

For more details about how to use the module, see the example notebook which utilizes multiple ALS for movie recommendation

Preliminary Results

Top-k (=10) recommendation performance metrics on MovieLens 100k dataset

• x-axis: Number of base models (ALS), M, in the bagging model
• Max: Max metric value among the M base models
• Min: Min metric value among the M base models
• Avg: Averaged metric values of the M base models
• Bagging: Ensemble results of the M base models