本节讲“矩阵”，“数组”

> M <- matrix(c(3:14),nrow=4,byrow=TRUE)
> print(M)
     [,1] [,2] [,3]
[1,]    3    4    5
[2,]    6    7    8
[3,]    9   10   11
[4,]   12   13   14

> M <- matrix(c(3:14),nrow=4,byrow=FALSE)
> print(M)
     [,1] [,2] [,3]
[1,]    3    7   11
[2,]    4    8   12
[3,]    5    9   13
[4,]    6   10   14

> N <- matrix(c(3:14),nrow=4,byrow=FALSE)
> print(N)
     [,1] [,2] [,3]
[1,]    3    7   11
[2,]    4    8   12
[3,]    5    9   13
[4,]    6   10   14

> #define the column and row names
> rownames = c("row1","row2","row3","row4")
> colnames = c("col1","col2","col3")

> p <- matrix(c(3:14),nrow = 4, byrow = TRUE, dimnames = list(rownames,colnames))
> print(p)
     col1 col2 col3
row1    3    4    5
row2    6    7    8
row3    9   10   11
row4   12   13   14

> #访问矩阵的元素
> # Access the element at 3rd column and 1st row.
> P <- matrix(c(3:14),nrow = 4, byrow = TRUE, dimnames = list(rownames,colnames))

> print(P)
     col1 col2 col3
row1    3    4    5
row2    6    7    8
row3    9   10   11
row4   12   13   14
> 
> # Access the element at 3rd column and 1st row.
> print(P[1,3])
[1] 5
> 
> # Access the element at 2nd column and 4th row.
> print(P[4,2])
[1] 13
> 
> # Access only the  2nd row.
> print(P[2,])
col1 col2 col3 
   6    7    8 
> 
> # Access only the 3rd column.
> print(P[,3])
row1 row2 row3 row4 
   5    8   11   14 

> #矩阵加法和减法
> # Create two 2x3 matrices.
> matrix1 <- matrix(c(3, 9, -1, 4, 2, 6), nrow = 2)
> print(matrix1)
     [,1] [,2] [,3]
[1,]    3   -1    2
[2,]    9    4    6
> 
> matrix2 <- matrix(c(5, 2, 0, 9, 3, 4), nrow = 2)
> print(matrix2)
     [,1] [,2] [,3]
[1,]    5    0    3
[2,]    2    9    4
> 
> # Add the matrices.
> result <- matrix1 + matrix2
> cat("Result of addition","
+ ")
Result of addition 
> print(result)
     [,1] [,2] [,3]
[1,]    8   -1    5
[2,]   11   13   10
> 
> # Subtract the matrices
> result <- matrix1 - matrix2
> cat("Result of subtraction","
+ ")
Result of subtraction 
> print(result)
     [,1] [,2] [,3]
[1,]   -2   -1   -1
[2,]    7   -5    2

> #矩阵乘法和除法
> # Create two 2x3 matrices.
> matrix1 <- matrix(c(3, 9, -1, 4, 2, 6), nrow = 2)
> print(matrix1)
     [,1] [,2] [,3]
[1,]    3   -1    2
[2,]    9    4    6
> 
> matrix2 <- matrix(c(5, 2, 0, 9, 3, 4), nrow = 2)
> print(matrix2)
     [,1] [,2] [,3]
[1,]    5    0    3
[2,]    2    9    4
> 
> # Multiply the matrices.
> result <- matrix1 * matrix2
> cat("Result of multiplication","
+ ")
Result of multiplication 
> print(result)
     [,1] [,2] [,3]
[1,]   15    0    6
[2,]   18   36   24
> 
> # Divide the matrices
> result <- matrix1 / matrix2
> cat("Result of division","
+ ")
Result of division 
> print(result)
     [,1]      [,2]      [,3]
[1,]  0.6      -Inf 0.6666667
[2,]  4.5 0.4444444 1.5000000
> 

数组

> #数组·
> #create two vectors of different lengths
> vector1 <- c(5,9)
> vector2 <- c(10,11,12,13,14,15)
> 
> result <- array(c(vector1,vector2),dim = c(3,3,2))
> print(result)
, , 1

     [,1] [,2] [,3]
[1,]    5   11   14
[2,]    9   12   15
[3,]   10   13    5

, , 2

     [,1] [,2] [,3]
[1,]    9   12   15
[2,]   10   13    5
[3,]   11   14    9


> vector1 <- c(5)
> vector2 <- c(10,11,12,13,14,15)
> result <- array(c(vector1,vector2),dim = c(3,3,2))
> print(result)
, , 1

     [,1] [,2] [,3]
[1,]    5   12   15
[2,]   10   13    5
[3,]   11   14   10

, , 2

     [,1] [,2] [,3]
[1,]   11   14   10
[2,]   12   15   11
[3,]   13    5   12



> # Create two vectors of different lengths.
> vector1 <- c(5,9,3)
> vector2 <- c(10,11,12,13,14,15)
> 
> # Take these vectors as input to the array.
> result <- array(c(vector1,vector2),dim = c(3,3,2))
> print(result)
, , 1

     [,1] [,2] [,3]
[1,]    5   10   13
[2,]    9   11   14
[3,]    3   12   15

, , 2

     [,1] [,2] [,3]
[1,]    5   10   13
[2,]    9   11   14
[3,]    3   12   15



> #命名列和行
> 我们可以使用dimnames参数给数组中的行，列和矩阵命名。> 我们可以使用dimnames参数给数组中的行，列和矩阵命名。

> #我们可以使用dimnames参数给数组中的行，列和矩阵命名。
> #create two vectors of different lengths
> vector1 <- c(5,9,3)
> vector2 <-c(10,12,13,14,15,16)
> column.names <- c("col1","col2","col3")
> row.names <- c("row1","row2","row3")
> matrix.names <- c("Matrix1","Matrix2")
> 
> #Take these vectors as input to the array
>  result <- array(c(vector1,vector2),dim=c(3,3,2),dimnames = list(row.names,column.names,matrix.names))
> print(result)
, , Matrix1

     col1 col2 col3
row1    5   10   14
row2    9   12   15
row3    3   13   16

, , Matrix2

     col1 col2 col3
row1    5   10   14
row2    9   12   15
row3    3   13   16


> #访问数组元素
> # Print the third row of the second matrix of the array.
> print(result[3,,2])
col1 col2 col3 
   3   13   16 
> 
> # Print the element in the 1st row and 3rd column of the 1st matrix.
> print(result[1,3,1])
[1] 14
> 
> # Print the 2nd Matrix.
> print(result[,,2])
     col1 col2 col3
row1    5   10   14
row2    9   12   15
row3    3   13   16
> 

> # Create two vectors of different lengths.
> vector1 <- c(5,9,3)
> vector2 <- c(10,11,12,13,14,15)
> 
> # Take these vectors as input to the array.
> new.array <- array(c(vector1,vector2),dim = c(3,3,2))
> print(new.array)
, , 1

     [,1] [,2] [,3]
[1,]    5   10   13
[2,]    9   11   14
[3,]    3   12   15

, , 2

     [,1] [,2] [,3]
[1,]    5   10   13
[2,]    9   11   14
[3,]    3   12   15

> # Use apply to calculate the sum of the rows across all the matrices.
> result <- apply(new.array, c(1), sum)
> print(result)
[1] 56 68 60

> # Use apply to calculate the sum of the columns across all the matrices.
> result <- apply(new.array, c(2),sum)
> print(result)
[1] 34 66 84
>