R语言矩阵知识点总结及实例分析

矩阵是其中元素以二维矩形布局布置的r对象。它们包含相同原子类型的元素。虽然我们可以创建一个只包含字符或只包含逻辑值的矩阵，但它们没有太多用处。我们使用包含数字元素的矩阵用于数学计算。

使用matrix()函数创建一个矩阵。

语法

在r语言中创建矩阵的基本语法是

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

以下是所使用的参数的说明

数据是成为矩阵的数据元素的输入向量。
nrow是要创建的行数。
ncol是要创建的列数。
byrow是一个逻辑线索。如果为true，则输入向量元素按行排列。
dimname是分配给行和列的名称。

例

创建一个以数字向量作为输入的矩阵

# elements are arranged sequentially by row.
m <- matrix(c(3:14), nrow = 4, byrow = true)
print(m)

# elements are arranged sequentially by column.
n <- matrix(c(3:14), nrow = 4, byrow = false)
print(n)

# 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)

当我们执行上面的代码，它产生以下结果 -

     [,1] [,2] [,3]
[1,]    3    4    5
[2,]    6    7    8
[3,]    9   10   11
[4,]   12   13   14
     [,1] [,2] [,3]
[1,]    3    7   11
[2,]    4    8   12
[3,]    5    9   13
[4,]    6   10   14
     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

可以通过使用元素的列和行索引来访问矩阵的元素。我们考虑上面的矩阵p找到下面的具体元素。

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

# create the matrix.
p <- matrix(c(3:14), nrow = 4, byrow = true, dimnames = list(rownames, colnames))

# access the element at 3rd column and 1st row.
print(p[1,3])

# access the element at 2nd column and 4th row.
print(p[4,2])

# access only the  2nd row.
print(p[2,])

# access only the 3rd column.
print(p[,3])

当我们执行上面的代码，它产生以下结果 -

[1] 5
[1] 13
col1 col2 col3 
   6    7    8 
row1 row2 row3 row4 
   5    8   11   14

矩阵计算

使用r运算符对矩阵执行各种数学运算。操作的结果也是一个矩阵。
对于操作中涉及的矩阵，维度（行数和列数）应该相同。

矩阵加法和减法

# create two 2x3 matrices.
matrix1 <- matrix(c(3, 9, -1, 4, 2, 6), nrow = 2)
print(matrix1)

matrix2 <- matrix(c(5, 2, 0, 9, 3, 4), nrow = 2)
print(matrix2)

# add the matrices.
result <- matrix1 + matrix2
cat("result of addition","
")
print(result)

# subtract the matrices
result <- matrix1 - matrix2
cat("result of subtraction","
")
print(result)

当我们执行上面的代码，它产生以下结果 -

     [,1] [,2] [,3]
[1,]    3   -1    2
[2,]    9    4    6
     [,1] [,2] [,3]
[1,]    5    0    3
[2,]    2    9    4
result of addition 
     [,1] [,2] [,3]
[1,]    8   -1    5
[2,]   11   13   10
result of subtraction 
     [,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)

matrix2 <- matrix(c(5, 2, 0, 9, 3, 4), nrow = 2)
print(matrix2)

# multiply the matrices.
result <- matrix1 * matrix2
cat("result of multiplication","
")
print(result)

# divide the matrices
result <- matrix1 / matrix2
cat("result of division","
")
print(result)

当我们执行上面的代码，它产生以下结果 -

     [,1] [,2] [,3]
[1,]    3   -1    2
[2,]    9    4    6
     [,1] [,2] [,3]
[1,]    5    0    3
[2,]    2    9    4
result of multiplication 
     [,1] [,2] [,3]
[1,]   15    0    6
[2,]   18   36   24
result of division 
     [,1]      [,2]      [,3]
[1,]  0.6      -inf 0.6666667
[2,]  4.5 0.4444444 1.5000000

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