Here is some essential reads for those that use R
Regression Modeling Strategies - F. Harrell http://www.springer.com/gb/book/9781441929181
Elements of Statistical Learning - Hastie et al https://statweb.stanford.edu/~tibs/ElemStatLearn/
Introduction to Statistical Learning - James et all http://www.springer.com/us/book/9781461471370
The Art of R Programming - N. Matloff https://www.nostarch.com/artofr.htm
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