Machine learning often requires us to think spatially and make choices about what it means for two instances to be close or far apart. So which is best - Euclidean? Manhattan? Cosine? It all depends! In this talk, we'll explore open source tools and visual diagnostic strategies for picking good distance metrics when doing machine learning on text.
Whether we're modeling irises, houses in Boston, photos of dogs, or comments on Reddit, machine learning requires us to quantify "distance" between our instances. To do this, we must first imagine that our condos or corgis are points in space, where the relative closeness of any two tells us how similar they are. For text analysis tasks like document classification and topic modeling, our choice of distance metric is particularly important! Why? Because text produces a very high dimensional space, with some features that are much more important than others. Moreover, text is often sparsely distributed, with some feature variations that are much more significant.
Great! So what metric should we use - Euclidean? Manhattan? Minkowski? Jaccard? Cosine? Unfortunately, no two corpora are created equal. The number of documents, their lengths, and vocabulary all significantly impact the distribution and shape of a data set. But while there's no perfect one-size-fits-all distance measure, we can use visual diagnostics to begin developing an intuition around distance metrics best suited to a particular problem. Visual diagnostics leverage one of our most powerful analytic tools — the human visual cortex — to identify patterns and signals that would otherwise be opaque with purely numeric outputs. The open source visual diagnostics library Yellowbrick is a tool for professional data scientists, engineers, and students to more easily visualize how data is fit and transformed throughout the machine learning process. Yellowbrick provides a visualization API modeled on scikit-learn's, providing
Visualizers to support feature analysis, model selection, and hyperparameter tuning.
In this talk, we'll see how to use Yellowbrick to visualize our corpora at both a micro and macro level. We'll begin at a very high level, using stochastic neighbor embedding plots to look at two-dimensional projections of our documents. As we experiment with different SciPy distance metrics, we can visualize their impact on the distribution of the data, for instance seeing how classes become more or less separable. Next, we can zoom in with token frequency distribution plots to explore feature importances (which in the context of text data will be n-grams). Once we've identified some of the n-grams we expect to be highly influential, we can filter for them using dispersion plots to see how they are distributed throughout the corpus and across documents of varying lengths. By the end of the talk, attendees will walk away with a visual intuition about how words can operate in space and with some new ideas about how to proceed with their own machine learning projects.