rowSums(x); colSums(x)；rowMeans(x); colMeans(x)

>  x2 = c(4:1, 2:5)

> x2

[1] 4 3 2 1 2 3 4 5

>  x <- cbind(x1 = 3, x2 = c(4:1, 2:5))

> x

     x1 x2

[1,]  3  4

[2,]  3  3

[3,]  3  2

[4,]  3  1

[5,]  3  2

[6,]  3  3

[7,]  3  4

[8,]  3  5

>  rowSums(x); colSums(x)

[1] 7 6 5 4 5 6 7 8

x1 x2 

24 24 

> rowMeans(x); colMeans(x)

[1] 3.5 3.0 2.5 2.0 2.5 3.0 3.5 4.0

x1 x2 

 3  3 

> rowSums(x) 横向加和

 colSums(x) 纵向加和

 rowMeans(x) 横向平均

 colMeans(x) 纵向平均