0. Introduction * Define the problems of classical filtering (e.g., news filtering, spam filtering) and collaborative filtering (e.g., recommendation systems). * Compare and contrast: predictions based upon features (spam filtering) vs. predictions based upon similar preferences (recommendation systems). * Look at real-world examples: SpamAssassin as used by CCIS; collaborative filtering at Amazon. 1. Filtering, e.g. spam. * Features and feature selection. * SpamAssassin. * Linear classifiers in general, and SpamAssassin as a linear classifier. * Positively and negatively correlated features. * Short introduction to training linear classifiers: separable data vs. non-separable data. * Evaluation: (1) simple error rates, (2) false positives vs. false negatives and the idea behind "utility functions" (though I never mentioned that phrase). 2. Collaborative filtering, e.g. recommendation systems. * Weighted combination of recommendations from "like minded" individuals. * How to assess "like mindedness?" Linear correlation coefficients. * Positive correlation vs. negative correlation vs. no correlation.
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