本书简单介绍了 S 语言（R 软件即是基于此）的基本入门知识。PDF 很清晰，是北大老师所写的内部（未出版）电子书。-Book is a brief introduction to the S language (R software that is based on this) the basic entry knowledge. PDF is very clear, is a university teacher written internal (unpublished) book.