library(readr)
data3_1 <- read_csv("data3.1.csv")View(data3_1)
lm5<-lm(y~.,data=data3_1)
lm6<-step(lm5,direction = "both")
summary(lm6)

输出：
Start:  AIC=377.73
y ~ x1 + x2 + x3 + x4 + x5 + x6 + x7 + x8 + x9Df Sum of Sq      RSS    AIC
- x4    1        21  3184326 375.73
- x9    1     17149  3201454 375.90
- x7    1     17700  3202005 375.90
- x8    1     54295  3238599 376.26
- x6    1     89586  3273891 376.59
<none>               3184305 377.73
- x3    1   2662593  5846898 394.57
- x2    1   4561056  7745361 403.29
- x5    1   9377500 12561805 418.28
- x1    1  23314547 26498852 441.42Step:  AIC=375.73
y ~ x1 + x2 + x3 + x5 + x6 + x7 + x8 + x9Df Sum of Sq      RSS    AIC
- x9    1     17428  3201754 373.90
- x7    1     18563  3202889 373.91
- x8    1     54437  3238763 374.2