Just a “heads-up.”
I’ve been editing a two-part series Nina Zumel is writing on some of the pitfalls of improperly applied principal components analysis/regression and how to avoid them (we are using the plural spelling as used in following Everitt The Cambridge Dictionary of Statistics). The series is looking absolutely fantastic and I think it will really help people understand, properly use, and even teach the concepts.
Frankly the material would have worked great as an additional chapter for Practical Data Science with R (but instead everybody is going to get it for free).
Please watch here for the series.