创建四个成份的列表：字符串、数值型向量、矩阵以及字符型向量。组合可以任意，最后保存为列表。
> g <- "My First List"
> h <- c(25,26,18,39)
> j <- matrix(1:10, nrow = 5)
> k <- c("one","two","three")
> mylist <- list(title=g,ages=h,j,k)
> mylist
$title
[1] "My First List"
$ages
[1] 25 26 18 39
[[3]]
[,1] [,2]
[1,] 1 6
[2,] 2 7
[3,] 3 8
[4,] 4 9
[5,] 5 10
[[4]]
[1] "one" "two" "three"
> mylist[[2]]
[1] 25 26 18 39
