1mydata <- data.fram(x1=c(1, 2, 3, 4), x2=c(5, 6, 7,8))
2mydata$meanx <- (mydata$x1 + mydata$x2)/2
3简化版1，#先绑定数据用attach
attach(mydata)
mydata$sumx < - x1 + x2
detach(mydata)
4用transform()函数
mydata <- transform(mydata, sumx =x1 + x2)