R 简明教程
R - Arrays
数组是 R 数据对象，它可以在两个以上维度中存储数据。例如，如果我们创建一个维度为 (2, 3, 4) 的数组，则会创建 4 个矩形矩阵，每个矩阵有 2 行和 3 列。数组只能存储数据类型。
Arrays are the R data objects which can store data in more than two dimensions. For example − If we create an array of dimension (2, 3, 4) then it creates 4 rectangular matrices each with 2 rows and 3 columns. Arrays can store only data type.
使用 array() 函数创建数组。它将向量作为输入，并使用 dim 参数中的值来创建数组。
An array is created using the array() function. It takes vectors as input and uses the values in the dim parameter to create an array.
Example
以下示例创建了两个 3x3 矩阵的数组，每个矩阵有 3 行和 3 列。
The following example creates an array of two 3x3 matrices each with 3 rows and 3 columns.
# Create two vectors of different lengths.
vector1 <- c(5,9,3)
vector2 <- c(10,11,12,13,14,15)
# Take these vectors as input to the array.
result <- array(c(vector1,vector2),dim = c(3,3,2))
print(result)当我们执行上述代码时，会产生以下结果 -
When we execute the above code, it produces the following result −
, , 1
[,1] [,2] [,3]
[1,] 5 10 13
[2,] 9 11 14
[3,] 3 12 15
, , 2
[,1] [,2] [,3]
[1,] 5 10 13
[2,] 9 11 14
[3,] 3 12 15Naming Columns and Rows
我们可以使用 dimnames 参数为数组中的行、列和矩阵命名。
We can give names to the rows, columns and matrices in the array by using the dimnames parameter.
# Create two vectors of different lengths.
vector1 <- c(5,9,3)
vector2 <- c(10,11,12,13,14,15)
column.names <- c("COL1","COL2","COL3")
row.names <- c("ROW1","ROW2","ROW3")
matrix.names <- c("Matrix1","Matrix2")
# Take these vectors as input to the array.
result <- array(c(vector1,vector2),dim = c(3,3,2),dimnames = list(row.names,column.names,
matrix.names))
print(result)当我们执行上述代码时，会产生以下结果 -
When we execute the above code, it produces the following result −
, , Matrix1
COL1 COL2 COL3
ROW1 5 10 13
ROW2 9 11 14
ROW3 3 12 15
, , Matrix2
COL1 COL2 COL3
ROW1 5 10 13
ROW2 9 11 14
ROW3 3 12 15Accessing Array Elements
# Create two vectors of different lengths.
vector1 <- c(5,9,3)
vector2 <- c(10,11,12,13,14,15)
column.names <- c("COL1","COL2","COL3")
row.names <- c("ROW1","ROW2","ROW3")
matrix.names <- c("Matrix1","Matrix2")
# Take these vectors as input to the array.
result <- array(c(vector1,vector2),dim = c(3,3,2),dimnames = list(row.names,
column.names, matrix.names))
# Print the third row of the second matrix of the array.
print(result[3,,2])
# Print the element in the 1st row and 3rd column of the 1st matrix.
print(result[1,3,1])
# Print the 2nd Matrix.
print(result[,,2])当我们执行上述代码时，会产生以下结果 -
When we execute the above code, it produces the following result −
COL1 COL2 COL3
3 12 15
[1] 13
COL1 COL2 COL3
ROW1 5 10 13
ROW2 9 11 14
ROW3 3 12 15Manipulating Array Elements
由于数组是由多维矩阵组成的，因此对数组元素的操作是通过访问矩阵的元素来执行的。
As array is made up matrices in multiple dimensions, the operations on elements of array are carried out by accessing elements of the matrices.
# Create two vectors of different lengths.
vector1 <- c(5,9,3)
vector2 <- c(10,11,12,13,14,15)
# Take these vectors as input to the array.
array1 <- array(c(vector1,vector2),dim = c(3,3,2))
# Create two vectors of different lengths.
vector3 <- c(9,1,0)
vector4 <- c(6,0,11,3,14,1,2,6,9)
array2 <- array(c(vector1,vector2),dim = c(3,3,2))
# create matrices from these arrays.
matrix1 <- array1[,,2]
matrix2 <- array2[,,2]
# Add the matrices.
result <- matrix1+matrix2
print(result)当我们执行上述代码时，会产生以下结果 -
When we execute the above code, it produces the following result −
[,1] [,2] [,3]
[1,] 10 20 26
[2,] 18 22 28
[3,] 6 24 30Calculations Across Array Elements
我们可以使用 apply() 函数对数组中的元素进行计算。
We can do calculations across the elements in an array using the apply() function.
Syntax
apply(x, margin, fun)以下是所用参数的描述 -
Following is the description of the parameters used −
-
x is an array.
-
margin is the name of the data set used.
-
fun is the function to be applied across the elements of the array.
Example
我们在下面使用 apply() 函数来计算跨所有矩阵的数组行中的元素的总和。
We use the apply() function below to calculate the sum of the elements in the rows of an array across all the matrices.
# Create two vectors of different lengths.
vector1 <- c(5,9,3)
vector2 <- c(10,11,12,13,14,15)
# Take these vectors as input to the array.
new.array <- array(c(vector1,vector2),dim = c(3,3,2))
print(new.array)
# Use apply to calculate the sum of the rows across all the matrices.
result <- apply(new.array, c(1), sum)
print(result)当我们执行上述代码时，会产生以下结果 -
When we execute the above code, it produces the following result −
, , 1
[,1] [,2] [,3]
[1,] 5 10 13
[2,] 9 11 14
[3,] 3 12 15
, , 2
[,1] [,2] [,3]
[1,] 5 10 13
[2,] 9 11 14
[3,] 3 12 15
[1] 56 68 60