The main motivation to dedicate an entire chapter on heat maps and dendrograms is to introduce the concept of clustering. We have also introduced tree maps toward the end of this chapter. Recently, I have observed the rising popularity of tree maps in news media and on financial websites.
Clustering techniques can be grouped into K mean clustering and hierarchical clustering. Dendrograms, a part of hierarchical clustering, are tree-like structures with branches and are used in visualization when we do not know the number of clusters in advance.
My first encounter with heat maps was an infographic published by the New York Times (http://www.nytimes.com/interactive/2012/06/11/sports/basketball/nba-shot-analysis.html?_r=0) about the points scored by basketball players playing for Miami Heat versus Oklahoma City Thunders. The infographic was created by Jeremy White, Joe Ward, and Mathew Ericson. Similar infographics can be constructed in R as well, but for the purpose of this chapter...