摘要：
### subset 函数 airquality <- airquality #选取Temp大于80的行，保留Ozone,temp两列 subset(airquality, Temp > 80, select = c(Ozone, Temp)) #选取day等于1的行，删去temp列 subset( 阅读全文
摘要：
ifelse returns a value with the same shape as test which is filled with elements selected from either yes or no depending on whether the element of te 阅读全文