矩陣是其中元素以二維矩形布局布置的R對(duì)象。 它們包含相同原子類型的元素。 雖然我們可以創(chuàng)建一個(gè)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(jì)算。
使用matrix()函數(shù)創(chuàng)建一個(gè)矩陣。
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。
nrow是要?jiǎng)?chuàng)建的行數(shù)。
ncol是要?jiǎng)?chuàng)建的列數(shù)。
byrow是一個(gè)邏輯線索。 如果為TRUE,則輸入向量元素按行排列。
dimname是分配給行和列的名稱。
創(chuàng)建一個(gè)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,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
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。
# 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,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
# 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
# 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,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
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