R Language

向量定义：x1 = c(1,2,3); x2 = c(1:100)

类型显示：mode(x1)

向量长度：length(x2)

向量元素显示：x1[c(1,2,3)]

多维向量：multi-dimensional vector：rbind(x1,x2); cbind(x1,x2)

 1 > x = c(1,2,3,4,5,6)
 2 > y = c(6,5,4,3,2,1)
 3 > z = rbind(x,y)
 4 > z
 5   [,1] [,2] [,3] [,4] [,5] [,6]
 6 x    1    2    3    4    5    6
 7 y    6    5    4    3    2    1
 8 > z = cbind(x,y)
 9 > z
10      x y
11 [1,] 1 6
12 [2,] 2 5
13 [3,] 3 4
14 [4,] 4 3
15 [5,] 5 2
16 [6,] 6 1
17 > 

一维变二维向量：

> mtx=matrix(1:12, nrow=3, ncol=4)
> mtx
     [,1] [,2] [,3] [,4]
[1,]    1    4    7   10
[2,]    2    5    8   11
[3,]    3    6    9   12

> mtx=matrix(1:12, nrow=3, ncol=4, byrow=T)
> mtx
     [,1] [,2] [,3] [,4]
[1,]    1    2    3    4
[2,]    5    6    7    8
[3,]    9   10   11   12

矩阵转置：

> mtx
     [,1] [,2] [,3] [,4]
[1,]    1    2    3    4
[2,]    5    6    7    8
[3,]    9   10   11   12
> t(mtx)
     [,1] [,2] [,3]
[1,]    1    5    9
[2,]    2    6   10
[3,]    3    7   11
[4,]    4    8   12

矩阵相乘：

> a = mtx%*%t(mtx)> a
     [,1] [,2] [,3]
[1,]   30   70  110
[2,]   70  174  278
[3,]  110  278  446

对角线矩阵：

> diag(a)
[1]  30 174 446

> diag(diag(a))
     [,1] [,2] [,3]
[1,]   30    0    0
[2,]    0  174    0
[3,]    0    0  446

> diag(3)
     [,1] [,2] [,3]
[1,]    1    0    0
[2,]    0    1    0
[3,]    0    0    1

逆矩阵：

> a = matrix(rnorm(16),4,4)
> a
           [,1]       [,2]      [,3]       [,4]
[1,]  0.5116868 -0.5839355 0.9038526 -1.5063944
[2,] -1.0657446 -2.2067686 1.2187536  0.1999609
[3,]  0.4784326 -2.1762163 0.1937103  0.0255462
[4,] -2.5393649 -0.1884904 2.7594314 -0.6955184

> solve(a)
           [,1]      [,2]     [,3]      [,4]
[1,] -1.7427160 -5.204571 5.530340 2.4812951
[2,] -0.6103805 -1.743684 1.396904 0.8719984
[3,] -2.2412701 -6.107496 6.505573 3.3373229
[4,] -2.3639756 -4.756515 5.240446 2.5072471

> solve(a)%*%a
              [,1]          [,2]          [,3]          [,4]
[1,]  1.000000e+00  2.390341e-15 -1.167469e-15  1.311885e-16
[2,]  5.746272e-17  1.000000e+00 -2.270319e-16  1.114018e-16
[3,] -2.550044e-16 -1.047339e-16  1.000000e+00 -1.275022e-16
[4,]  5.872039e-16 -1.514197e-15 -7.502679e-17  1.000000e+00

平均值：mean(x1)

求和：sum(x1)

最大值：max(x1)

最小值：min(x1)

方差：var(x1)

标准差：sd(x1)

累乘：prod(x1)

> seq(5, 10, by=2)
[1] 5 7 9

> seq(5, 50, length=13)
 [1]  5.00  8.75 12.50 16.25 20.00 23.75 27.50 31.25 35.00 38.75 42.50 46.25
[13] 50.00

字母向量

> letters
 [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r"
[19] "s" "t" "u" "v" "w" "x" "y" "z"

> letters[1:4]
[1] "a" "b" "c" "d"

> letters[1:30]
 [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r"
[19] "s" "t" "u" "v" "w" "x" "y" "z" NA  NA  NA  NA

下标函数：which()

> a=c(2,3,4,5,6,7,2,3,4,8,9,5)

> which.max(a)
[1] 11

> which(a==2)
[1] 1 7

> which(a>3)
[1]  3  4  5  6  9 10 11 12

> a[which(a>3)]
[1] 4 5 6 7 4 8 9 5

向量排序：rev(x), sort(x)