Lately, I've been thinking about the topic of reducing the number of variables, and how this is a lot like clustering variables (rather than clustering rows). This post is about a method that seems intuitive to me, although I haven't found any references to it. Perhaps a reader will point me to references and a formal name. This method using Pearson correlation and principal components to agglomeratively cluster the variables.
Agglomerative clustering is the process of ass