統計分析：使用 R/R/矩陣的介紹
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許多統計理論使用矩陣代數。雖然本書不需要詳細瞭解矩陣，但瞭解 R 如何處理矩陣非常有用。
本質上，矩陣（複數：矩陣）是向量的二維等價物。換句話說，它是一個數字的矩形網格，按行和列排列。在 R 中，可以使用matrix()函式建立矩陣物件，該函式將一個數字向量（用於填充矩陣）作為第一個引數，並將行數和列數分別作為第二個和第三個引數。
R 也可以使用陣列物件，它們類似於矩陣，但可以有超過 2 個維度。這些對於表格特別有用：一種包含根據各種標準分類的資料計數的陣列。這些“列聯表”的示例如下所示的HairEyeColor和Titanic表。
[]可用於訪問矩陣或陣列中的單個元素或元素集。這是透過用逗號分隔括號內的數字來完成的。例如，對於矩陣，需要指定行索引，然後是一個逗號，然後是列索引。如果行索引為空，則假定需要所有行，列索引也是如此。
輸入m <- matrix(1:12, 3, 4) #Create a 3x4 matrix filled with numbers 1 to 12
m #Display it!
m*2 #Arithmetic, just like with vectors
m[2,3] #Pick out a single element (2nd row, 3rd column)
m[1:2, 2:4] #Or a range (rows 1 and 2, columns 2, 3, and 4.)
m[,1] #If the row index is missing, assume all rows
m[1,] #Same for columns
m[,2] <- 99 #You can assign values to one or more elements
m #See!
###Some real data, stored as "arrays"
HairEyeColor #A 3D array
HairEyeColor[,,1] #Select only the males to make it a 2D matrix
Titanic #A 4D array
Titanic[1:3,"Male","Adult",] #A matrix of only the adult male passengers
結果> m <- matrix(1:12, 3, 4) #Create a 3x4 matrix filled with numbers 1 to 12
> m #Display it!
[,1] [,2] [,3] [,4]
[1,] 1 4 7 10
[2,] 2 5 8 11
[3,] 3 6 9 12
> m*2 #Arithmetic, just like with vectors
[,1] [,2] [,3] [,4]
[1,] 2 8 14 20
[2,] 4 10 16 22
[3,] 6 12 18 24
> m[2,3] #Pick out a single element (2nd row, 3rd column)
[1] 8
> m[1:2, 2:4] #Or a range (rows 1 and 2, columns 2, 3, and 4.)
[,1] [,2] [,3]
[1,] 4 7 10
[2,] 5 8 11
> m[,1] #If the row index is missing, assume all rows
[1] 1 2 3
> m[1,] #Same for columns
[1] 1 4 7 10
> m[,2] <- 99 #You can assign values to one or more elements
> m #See!
[,1] [,2] [,3] [,4]
[1,] 1 99 7 10
[2,] 2 99 8 11
[3,] 3 99 9 12
> ###Some real data, stored as "arrays"
> HairEyeColor #A 3D array
, , Sex = Male
Eye
Hair Brown Blue Hazel Green
Black 32 11 10 3
Brown 53 50 25 15
Red 10 10 7 7
Blond 3 30 5 8
, , Sex = Female
Eye
Hair Brown Blue Hazel Green
Black 36 9 5 2
Brown 66 34 29 14
Red 16 7 7 7
Blond 4 64 5 8
> HairEyeColor[,,1] #Select only the males to make it a 2D matrix
Eye
Hair Brown Blue Hazel Green
Black 32 11 10 3
Brown 53 50 25 15
Red 10 10 7 7
Blond 3 30 5 8
> Titanic #A 4D array
, , Age = Child, Survived = No
Sex
Class Male Female
1st 0 0
2nd 0 0
3rd 35 17
Crew 0 0
, , Age = Adult, Survived = No
Sex
Class Male Female
1st 118 4
2nd 154 13
3rd 387 89
Crew 670 3
, , Age = Child, Survived = Yes
Sex
Class Male Female
1st 5 1
2nd 11 13
3rd 13 14
Crew 0 0
, , Age = Adult, Survived = Yes
Sex
Class Male Female
1st 57 140
2nd 14 80
3rd 75 76
Crew 192 20
> Titanic[1:3,"Male","Adult",] #A matrix of only the adult male passengers
Survived
Class No Yes
1st 118 57
2nd 154 14
3rd 387 75