R语言--矩阵和数组

1矩阵的创建

函数： m <- matrix(1:20,nrow=4,ncol=5)
m2 <- matrix(1:20,4,5) 两种写法
表示数值从1到20 创建4行5列的矩阵

> x <-1:20
> x
 [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20
> m <- matrix(x,nrow=4,ncol=5)
> m
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    5    9   13   17
[2,]    2    6   10   14   18
[3,]    3    7   11   15   19
[4,]    4    8   12   16   20
> m2 <- matrix(1:20,4,5)
> m2
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    5    9   13   17
[2,]    2    6   10   14   18
[3,]    3    7   11   15   19
[4,]    4    8   12   16   20
> m2 <- matrix(1:20,5,5)
> m2
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    6   11   16    1
[2,]    2    7   12   17    2
[3,]    3    8   13   18    3
[4,]    4    9   14   19    4
[5,]    5   10   15   20    5
> m2 <- matrix(1:20,4,6)#报错
Warning message:
In matrix(1:20, 4, 6) :
  data length [20] is not a sub-multiple or multiple of the number of columns [6]
> m3 <- matrix(1:20,3,3)#报错
Warning message:
In matrix(1:20, 3, 3) :
  data length [20] is not a sub-multiple or multiple of the number of rows [3]
  #可以只写一个数  表示多少行列数会自动分配
> m4 <- matrix(1:20,4)
> m4
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    5    9   13   17
[2,]    2    6   10   14   18
[3,]    3    7   11   15   19
[4,]    4    8   12   16   20
#byrow=T  T表示前面给的数是固定行  F表示前面给的数固定列**
> m3 <- matrix(1:20,4,byrow=T)
> m3
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    2    3    4    5
[2,]    6    7    8    9   10
[3,]   11   12   13   14   15
[4,]   16   17   18   19   20

rname，cnames分别创建了行和列的名字
dimnames(m)<-list(rname,cnames)函数给矩阵赋予一个名字
可以用名字访问改矩阵

数组

数组（array）与矩阵类似，但是维度可以大于2。数组可通过array函数创建，形式如下：

myarray <- array(vector, dimensions, dimnames)

其中vector包含了数组中的数据，dimensions是一个数值型向量，给出了各个维度下标的最大值，而dimnames是可选的、各维度名称标签的列表。
也可用创建函数：dim()
下面代码构建了一个3维数组

> y <-1:20
> dim(y)<-c(2,2,5)
> y
, , 1

     [,1] [,2]
[1,]    1    3
[2,]    2    4

, , 2

     [,1] [,2]
[1,]    5    7
[2,]    6    8

, , 3

     [,1] [,2]
[1,]    9   11
[2,]   10   12

, , 4

     [,1] [,2]
[1,]   13   15
[2,]   14   16

, , 5

     [,1] [,2]
[1,]   17   19
[2,]   18   20

使用array创建带有标签名的数组

> dim1<- c("A1","A2","A3")
> dim2 <- c("B1","B2","B3")
> dim3<-c("C1","C2","C3","C4")

> z <- array(1:36, c(3, 3, 4), dimnames=list(dim1, dim2, dim3))
> z
, , C1

   B1 B2 B3
A1  1  4  7
A2  2  5  8
A3  3  6  9

, , C2

   B1 B2 B3
A1 10 13 16
A2 11 14 17
A3 12 15 18

, , C3

   B1 B2 B3
A1 19 22 25
A2 20 23 26
A3 21 24 27

, , C4

   B1 B2 B3
A1 28 31 34
A2 29 32 35
A3 30 33 36

矩阵的索引

矩阵可由向量转换得到，所以矩阵原则上用向量的索引方法
由于矩阵是管理二维数据的，所以使用两个下标便可以表示矩阵中的元素
矩阵索引与向量索引类似，也是使用下标和方括号来选择矩阵中的行、列或者元素

> m<-matrix(1:20,4,5,byrow=T)
> m
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    2    3    4    5
[2,]    6    7    8    9   10
[3,]   11   12   13   14   15
[4,]   16   17   18   19   20
#输出第二行第三列的数值
> m[2,3]
[1] 8
#输出第一行
> m[1,]
[1] 1 2 3 4 5
输出第一行第二到四列
> m[1,c(2:4)]
[1] 2 3 4
输出第二行第三行第二到五列
> m[c(2,3),c(2:5)]
     [,1] [,2] [,3] [,4]
[1,]    7    8    9   10
[2,]   12   13   14   15
第二行第一列的数字
> m[2]
[1] 6
去除掉第一行的第二列剩余的数字
> m[-1,2]
[1]  7 12 17

矩阵的运算

> m+1
     [,1] [,2] [,3] [,4] [,5]
[1,]    2    3    4    5    6
[2,]    7    8    9   10   11
[3,]   12   13   14   15   16
[4,]   17   18   19   20   21
> m
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    2    3    4    5
[2,]    6    7    8    9   10
[3,]   11   12   13   14   15
[4,]   16   17   18   19   20

两个矩阵行数和列数不同不能相加

> m
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    2    3    4    5
[2,]    6    7    8    9   10
[3,]   11   12   13   14   15
[4,]   16   17   18   19   20
> n<-matrix(1:20,5,4,byrow=T)
> n
     [,1] [,2] [,3] [,4]
[1,]    1    2    3    4
[2,]    5    6    7    8
[3,]    9   10   11   12
[4,]   13   14   15   16
[5,]   17   18   19   20
> m+n
Error in m + n : non-conformable arrays
每一行的和
> colSums(m)
[1] 34 38 42 46 50
每一行的平均值
> colMeans(m)
[1]  8.5  9.5 10.5 11.5 12.5
每一列的和
> rowSums(m)
[1] 15 40 65 90