R语言矩阵

矩阵是元素布置成二维矩形布局的R对象。 它们包含相同原子类型的元素。

R创建矩阵的语法：

matrix(data, nrow, ncol, byrow, dimnames)

参数说明：

• data - 成为矩阵的数据元素输入向量。
• nrow - 是要创建的行数。
• ncol -  要被创建的列数。
• byrow - 是一个合乎逻辑。若为True，则输入向量元素按行安排。
• dimnames - 是分配给行和列名称。

Example

> # Elements are arranged sequentially by row.
> M <- matrix(c(1:12), nrow=4, byrow=TRUE)
> print(M)
     [,1] [,2] [,3]
[1,]    1    2    3
[2,]    4    5    6
[3,]    7    8    9
[4,]   10   11   12
> # Elements are arranged sequentially by column.
> N <- matrix(c(1:12), nrow=4, byrow=FALSE)
> print(N)
     [,1] [,2] [,3]
[1,]    1    5    9
[2,]    2    6   10
[3,]    3    7   11
[4,]    4    8   12
> # Define the column and row names.
> rownames = c("row1", "row2", "row3", "row4")
> colnames = c("col1", "col2", "col3")
> P <- matrix(c(1:12), nrow=4, byrow=TRUE, dimnames=list(rownames, colnames))
> print(P)
     col1 col2 col3
row1    1    2    3
row2    4    5    6
row3    7    8    9
row4   10   11   12

访问矩阵：

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

矩阵计算：

> # 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","n")
Result of addition n
> print(result)
     [,1] [,2] [,3]
[1,]    8   -1    5
[2,]   11   13   10
> # Subtract the matrices
> result <- matrix1 - matrix2
> cat("Result of subtraction","n")
Result of subtraction n
> print(result)
     [,1] [,2] [,3]
[1,]   -2   -1   -1
[2,]    7   -5    2
> # Multiply the matrices.
> result <- matrix1 * matrix2
> cat("Result of multiplication","n")
Result of multiplication n
> print(result)
     [,1] [,2] [,3]
[1,]   15    0    6
[2,]   18   36   24
> # Divide the matrices
> result <- matrix1 / matrix2
> cat("Result of division","n")
Result of division n
> print(result)
     [,1]      [,2]      [,3]
[1,]  0.6      -Inf 0.6666667
[2,]  4.5 0.4444444 1.5000000

参考网址：http://www.phperz.com/special/109.html