Hierarchical clustering is often used with heatmaps and with machine learning type stuff. It's no big deal, though, and based on just a few simple concepts. If you want to draw a heatmap using R, I've put some sample code on my webiste: For a complete index of all the StatQuest videos, check out: If you'd like to support StatQuest, please consider... Patreon: ...or... YouTube Membership: ...buying one of my books, a study guide, a t-shirt or hoodie, or a song from the StatQuest store... ...or just donating to StatQuest! Lastly, if you want to keep up with me as I research and create new StatQuests, follow me on twitter: #statquest #ML #clustering