矩陣是其中元素以二維矩形布局布置的R對象。 它們包含相同原子類型的元素荒给。 雖然我們可以創(chuàng)建一個只包含字符或只包含邏輯值的矩陣，但它們沒有太多用處。 我們使用包含數(shù)字元素的矩陣用于數(shù)學(xué)計算扛吞。
使用matrix()函數(shù)創(chuàng)建一個矩陣。
語法
在R語言中創(chuàng)建矩陣的基本語法是 -
matrix(data, nrow, ncol, byrow, dimnames)
以下是所使用的參數(shù)的說明 -
數(shù)據(jù)是成為矩陣的數(shù)據(jù)元素的輸入向量荆责。
nrow是要創(chuàng)建的行數(shù)滥比。
ncol是要創(chuàng)建的列數(shù)。
byrow是一個邏輯線索做院。 如果為TRUE盲泛，則輸入向量元素按行排列。
dimname是分配給行和列的名稱键耕。
例
創(chuàng)建一個以數(shù)字向量作為輸入的矩陣
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(dāng)我們執(zhí)行上面的代碼寺滚，它產(chǎn)生以下結(jié)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
訪問矩陣的元素
可以通過使用元素的列和行索引來訪問矩陣的元素。 我們考慮上面的矩陣P找到下面的具體元素屈雄。
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(dāng)我們執(zhí)行上面的代碼村视，它產(chǎn)生以下結(jié)果 -
[1] 5
[1] 13
col1 col2 col3
6 7 8
row1 row2 row3 row4
5 8 11 14
矩陣計算
使用R運(yùn)算符對矩陣執(zhí)行各種數(shù)學(xué)運(yùn)算。 操作的結(jié)果也是一個矩陣酒奶。
對于操作中涉及的矩陣蚁孔，維度（行數(shù)和列數(shù)）應(yīng)該相同奶赔。
矩陣加法和減法
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)
當(dāng)我們執(zhí)行上面的代碼，它產(chǎn)生以下結(jié)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)
當(dāng)我們執(zhí)行上面的代碼杠氢，它產(chǎn)生以下結(jié)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
