数组是R数据对象,可以在两个以上的维度存储数据.例如 : 如果我们创建一个维度数组(2,3,4),那么它会创建4个矩形矩阵,每个矩阵有2行3列.数组只能存储数据类型.
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.
示例
以下示例创建一个包含3个3列和3列的两个3x3矩阵的数组.
# 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)
当我们执行上面的代码时,它产生以下结果 :
, , 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
命名列和行
我们可以为行命名,数组中的列和矩阵使用 dimnames 参数.
# 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)
当我们执行上面的代码时,它产生以下结果 :
, , Matrix1 COL1 COL2 COL3ROW1 5 10 13ROW2 9 11 14ROW3 3 12 15, , Matrix2 COL1 COL2 COL3ROW1 5 10 13ROW2 9 11 14ROW3 3 12 15
访问数组元素
# 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])
当我们执行上面的代码时,它产生以下结果 :
COL1 COL2 COL3 3 12 15 [1] 13 COL1 COL2 COL3ROW1 5 10 13ROW2 9 11 14ROW3 3 12 15
操纵数组元素
由于数组是由多个维构成矩阵,对数组元素的操作是通过访问矩阵的元素来执行的.
# 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+matrix2print(result)
当我们执行上面的代码时,会产生以下结果 : ;
[,1] [,2] [,3][1,] 10 20 26[2,] 18 22 28[3,] 6 24 30
跨数组元素的计算
我们可以使用 apply()函数对数组中的元素进行计算.
语法
apply(x, margin, fun)
以下是所用参数的描述 :
x 是一个数组.
margin 是所用数据集的名称.
fun 是要应用于整个数组的元素.
示例
我们使用下面的apply()函数来计算al的数组行中元素的总和l矩阵.
# 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)
执行时上面的代码,它产生以下结果 :
, , 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