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Array Operations in R Programming
  • Last Updated : 22 Apr, 2020

Arrays are the R data objects which store the data in more than two dimensions. Arrays are n-dimensional data structures. For example, if we create an array of dimensions (2, 3, 3) then it creates 3 rectangular matrices each with 2 rows and 3 columns. They are homogeneous data structures.

Now, let’s see how to create arrays in R. To create an array in R you need to use the function called array(). The arguments to this array() are the set of elements in vectors and you have to pass a vector containing the dimensions of the array.

Array_NAME <- array(data, dim = (row_Size, column_Size, matrices, dimnames)

where,

data – An input vector given to the array.
matrices – Consists of multi-dimensional matrices.
row_Size – Number of row elements that an array can store.
column_Size – Number of column elements that an array can store.
dimnames – Used to change the default names of rows and columns according to the user’s preference.

Example:






# Create the vectors with different length
vector1 <- c(1, 2, 3)
vector2 <- c(10, 15, 3, 11, 16, 12)
  
# taking this vector as input
result <- array(c(vector1, vector2), dim = c(3, 3, 2))
print(result)

Output:

, , 1

     [,1] [,2] [,3]
[1,]    1   10   11
[2,]    2   15   16
[3,]    3    3   12

, , 2

     [,1] [,2] [,3]
[1,]    1   10   11
[2,]    2   15   16
[3,]    3    3   12

Operations on Arrays

Naming columns and rows

We can give names to the rows and columns using dimnames.
Example:




# Creating Vectors
vector1 <- c(1, 2, 3)
vector2 <- c(10, 15, 3, 11, 16, 12)
  
# Giving Names to rows and columns
column.names <- c("COLUMN1", "COLUMN2", "COLUMN3")
row.names <- c("ROW1", "ROW2", "ROW3")
matrix.names <- c("Matrix.NO1", "Matrix.NO2")
  
# taking this vector as input
result <- array(c(vector1, vector2), dim = c(3, 3, 2), 
                  dimnames = list(row.names, column.names, matrix.names))
print(result)

Output:

, , Matrix.NO1

     COLUMN1 COLUMN2 COLUMN3
ROW1       1      10      11
ROW2       2      15      16
ROW3       3       3      12

, , Matrix.NO2

     COLUMN1 COLUMN2 COLUMN3
ROW1       1      10      11
ROW2       2      15      16
ROW3       3       3      12

Manipulating array elements

An array is made up of multiple dimensions and the operations are carried out by accessing elements.

Example:




# creating two vectors of different length
# and taking vector as input
vector1 <- c(1, 2, 3)
vector2 <- c(4, 6, 8, 0, 2, 4)
array1 <- array(c(vector1, vector2), dim = c(3, 3, 2))
  
# creating other array
vector3 <- c(3, 2, 1)
vector4 <- c(2, 4, 6, 8, 3, 5)
array2 <- array(c(vector3, vector4), dim = c(3, 3, 2))
  
# create matrices and add them
matrix1 <- array1[,,2]
matrix2 <- array2[,,2]
result <- matrix1 + matrix2
print(result)

Output:

     [,1] [,2] [,3]
[1,]    4    6    8
[2,]    4   10    5
[3,]    4   14    9

Accessing Array elements

Using index position in matrix any element can be accessed easily. Also, we can alter/change the element in an array using index position.
Syntax:

Array_Name[row_position, Column_Position, Matrix_Level]

Example:






# Creating Vectors
vector1 <- c(1, 2, 3)
vector2 <- c(10, 15, 3, 11, 16, 12)
column.names <- c("COLUMN1", "COLUMN2", "COLUMN3")
row.names <- c("ROW1", "ROW2", "ROW3")
matrix.names <- c("Matrix.NO1", "Matrix.NO2")
  
# taking vector as input
result <- array(c(vector1, vector2), dim = c(3, 3, 2), 
                  dimnames = list(row.names, column.names, matrix.names))
print(result)
  
# print third row of second matrix
print(result[3,,2])

Output:

, , Matrix.NO1

     COLUMN1 COLUMN2 COLUMN3
ROW1       1      10      11
ROW2       2      15      16
ROW3       3       3      12

, , Matrix.NO2

     COLUMN1 COLUMN2 COLUMN3
ROW1       1      10      11
ROW2       2      15      16
ROW3       3       3      12

COLUMN1 COLUMN2 COLUMN3 
      3       3      12 

Calculation across array element

apply() function is used for calculations across array elements.

Syntax:

apply(x, margin, fun)

where,
x – an array.
margin – name of the dataset used.
fun – function to be applied to the elements of the array.

Example:




# create two vectors and take them as input in array
vector1 <- c(3, 2, 1)
vector2 <- c(2, 4, 6, 8, 0, 1)
new.array <- array(c(vector1, vector2), dim = c(3, 3, 2))
print(new.array)
  
# using apply and calculate the sum of rows in matrices
result <- apply(new.array, c(1), sum)
print(result)

Output:

, , 1

     [,1] [,2] [,3]
[1,]    3    2    8
[2,]    2    4    0
[3,]    1    6    1

, , 2

     [,1] [,2] [,3]
[1,]    3    2    8
[2,]    2    4    0
[3,]    1    6    1

[1] 26 12 16

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