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(:), nrow=, byrow=TRUE)
> print(M)
     [,] [,] [,]
[,]
[,]
[,]
[,]
> # Elements are arranged sequentially by column.
> N <- matrix(c(:), nrow=, byrow=FALSE)
> print(N)
     [,] [,] [,]
[,]
[,]
[,]
[,]
> # Define the column and row names.
> rownames = c("row1", "row2", "row3", "row4")
> colnames = c("col1", "col2", "col3")
> P <- matrix(c(:), nrow=, byrow=TRUE, dimnames=list(rownames, colnames))
> print(P)
     col1 col2 col3
row1
row2
row3
row4         

访问矩阵：

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

矩阵计算：

> # Create two 2x3 matrices.
> matrix1 <- matrix(c(, , -, , , ), nrow=)
> print(matrix1)
     [,] [,] [,]
[,]       -
[,]
> matrix2 <- matrix(c(, , , , , ), nrow=)
> print(matrix2)
     [,] [,] [,]
[,]
[,]
> # Add the matrices.
> result <- matrix1 + matrix2
> cat("Result of addition","n")
Result of addition n
> print(result)
     [,] [,] [,]
[,]       -
[,]
> # Subtract the matrices
> result <- matrix1 - matrix2
> cat("Result of subtraction","n")
Result of subtraction n
> print(result)
     [,] [,] [,]
[,]   -   -   -
[,]       -
> # Multiply the matrices.
> result <- matrix1 * matrix2
> cat("Result of multiplication","n")
Result of multiplication n
> print(result)
     [,] [,] [,]
[,]
[,]
> # Divide the matrices
> result <- matrix1 / matrix2
> cat("Result of division","n")
Result of division n
> print(result)
     [,]      [,]      [,]
[,]  0.6      -Inf 0.6666667
[,]  4.5 0.4444444 1.5000000

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