矩陣是其中元素以二維矩形布局排列的R物件。它們包含相同原子型別的元素。 雖然我們可以建立一個僅包含字元或僅包含邏輯值的矩陣，但它們沒有太多用處。 我們使用包含數學元素的矩陣來在數學計算中使用。
矩陣可通過使用matrix()函式來建立。
在R中建立矩陣的基本語法是 -
matrix(data, nrow, ncol, byrow, dimnames)
以下是使用的引數的描述 -
建立一個使用數位向量作為輸入的矩陣，參考以下程式碼 -
# 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)
當我們執行上述程式碼時，會產生以下結果 -
[,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
可以使用元素的列和行索引來存取矩陣的元素。 我們考慮上面的矩陣P來找到下面的具體元素。
# 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])
當我們執行上述程式碼時，會產生以下結果 -
[1] 5
[1] 13
col1 col2 col3
6 7 8
row1 row2 row3 row4
5 8 11 14
使用R運算子對矩陣執行各種數學運算，操作的結果也是一個矩陣。
操作中涉及的矩陣的尺寸(行數和列數)應相同。
矩陣加法與減法運算範例 -
# 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","\n")
print(result)
# Subtract the matrices
result <- matrix1 - matrix2
cat("Result of subtraction","\n")
print(result)
當我們執行上述程式碼時，會產生以下結果 -
[,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
矩陣乘法與除法運算範例
# 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","\n")
print(result)
# Divide the matrices
result <- matrix1 / matrix2
cat("Result of division","\n")
print(result)
當我們執行上述程式碼時，會產生以下結果 -
[,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