K-means, Agglomerative, Silhouette Coefficient, Silhouette Score, Unsupervised Learning, Density-based clustering, DBSCAN, OPTICS — This article is a part of “Data Science from Scratch — Can I to I Can”, A Lecture Notes Book Series (Part-3). (click here to get your copy of Part-1 & Part-2 today) Click here for the previous article/lecture on “A46: Evaluating Clustering Algorithm — Unsupervised Machine Learning”.