摘要:
一 data structure 1.vector: a single entity consisting of an ordered collection of numbers x <- c(10.4, 5.6, 3.1, 6.4, 21.7) 等价于 c(10.4, 5.6, 3.1, 6.4, 阅读全文
摘要:
Some people think that printed books are no longer needed in a digital era because all writing can be stored electronically. Others think that printed 阅读全文