Jul 25, 2013 — Flatten 3D Data to Vector, and back to 3D in R — There is surprisingly little help online about how to flatten some 3D data, and then “unflatten” it back to its original size. Why would you want this functionality? Many machine learning algorithms that work with images treat pixel values as... Read more

Jul 24, 2013 — Archetypal Analysis — Archetypal Analysis is an unsupervised learning algorithm that postulates that each of our set of observations is some combination of some number, K, “pure subtypes,” or archetypes.  I’ll also refer to these as prototypes.  In the simple case of adult human... Read more

Jul 24, 2013 — Non-Negative Matrix Factorization — Non-negative matrix factorization (nnmf) is an unsupervised machine learning method for (you predicted it, strictly positive) data!  The goal of nnmf, of course, is dimensionality reduction.  We start with a dataset, X (size N x p), and want to decompose... Read more

Jul 24, 2013 — Sparse K-Means Clustering "Sparcl" — Tibshirani and Witten introduced a variation of K-Means clustering called “Sparcl.”  What gives it this name?  It is a method of sparse clustering that clusters with an adaptively chosen set of features, by way of the lasso penalty.  This method... Read more