生成向量的常用方法

c(2,5,6,2,9) 

## [1] 2 5 6 2 9

c("a","f","m","b")

## [1] "a" "f" "m" "b"

1:5

## [1] 1 2 3 4 5

rep("x",times=3)        #把"x"重复3次，组成一个向量

## [1] "x" "x" "x"

seq(from=3,to=21,by=3)  #从3到21，每3个数取1个数，组成一个向量

## [1]  3  6  9 12 15 18 21

rnorm(n=3)              #生成3个随机数，组成一个向量

## [1] -1.238104  1.074730 -1.797385

paste0(rep("x",times=3),1:3)

## [1] "x1" "x2" "x3"