Beginner's Guide to K-Nearest Neighbors in R: from Zero to Hero

In the world of Machine Learning, I find the K-Nearest Neighbors (KNN) classifier makes the most intuitive sense and easily accessible to beginners even without introducing any math notations. To decide the label of an observation, we look at its neighbors and assign the neighbors' label to the observation of interest. Certainly, looking at one neighbor may create bias and inaccuracy, and the KNN method has a set of rules and procedures to determine the best number of neighbors, e.g., examining k 1 neighbors and adopt majority rule to decide the category. "To decide the label for new observations, we look at the closest neighbors." To choose the nearest neighbors, we have to define what distance is.