## Introduction to Arrays in R

As we know, arrays are the objects that can store two or more than two-dimensional data. In R, Array has the same concept, which is created using the array() function. Here data gets stored in form matrices, rows and columns. In order to access a specific element from array, one needs to specify row index, column index, and matrix level.

Matrices frequently used in R, is special type of 2-D array.

**Pictorial representation: Vector, Matrix, Array**

- One dimensional array referred to as a vector.
- Two-dimensional array referred to as a matrix.

**Syntax:**

Here is the syntax of array:

`Array_NAME <- `

**array**(data, dim = (row_Size, column_Size, matrices, dimnames)

- data – Data is an input vector that is fed to the array.
- matrices – This refers to the dimensionality of matrices. Array in R can be multi-dimensional matrices.
- row_Size – row_Size depicts the number of rows that an array will comprise of.
- column_Size – column_Size depicts the number of columns that an array will comprise of.
- dimnames – This field if for changing the default names of rows and columns to the user’s wish/preference.

**Properties:**

- It’s homogeneous. That means it can store the same type of data.
- It stores data in contiguous memory
- Array elements can be accessed by knowing the index number.

### How to Create an array in R?

Below are different scenarios on how to create an array in r as follows:

#### Scenario 1:

Let’s create an array which would be 3×4 matrices. Here 3 will row and 4 will be columns, matrices will be one. As our initial steps, let’s keep dimnames = NULL(which is a default value, if nothing specified ).

This is a one-dimensional matrix

**R Code:**

`vector1 <- c(2,18,30)`

vector2 <- c(10,14,17,13,11,15,22,11,33)

print(array(c(vector1, vector2),dim = c(3,4,1)))

**Output:**

In order to check if finally created array got created or not.

Once array gets created:

**Result **

<- array(c(vector1, vector2),dim = c(3,4,1)))

The function “class” can help you with that.

class(Result)

**R Code:**

`vector1 <- c(2,18,30)`

vector2 <- c(10,14,17,13,11,15,22,11,33)

print(array(c(vector1, vector2),dim = c(3,4,1)))

Result <- array(c(vector1, vector2),dim = c(3,4,1))

class(Result)

**Output:**

In order to check the dimension’s product of the array, one can use function: length.

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**R Code:**

`vector1 <- c(2,18,30)`

vector2 <- c(10,14,17,13,11,15,22,11,33)

print(array(c(vector1, vector2),dim = c(3,4,1)))

Result <- array(c(vector1, vector2),dim = c(3,4,1))

length(Result)

**Output:**

#### Scenario 2:

Let’s create the same array which would be 3×4 matrices. Here again, 3 will be a row and 4 will be columns, but matrices will be two. Let’s keep dimnames = NULL(which is a default value, if nothing specified ).

**R code:**

`vector1 <- c(2,18,30)`

vector2 <- c(10,14,17,13,11,15,22,11,33)

print(array(c(vector1,vector2),dim = c(3,4,2)))

**Output:**

#### Scenario 3:

Let’s create the same array which would be 3×4 matrices. Here again, 3 will be row and 4 will be columns, but matrices will be two. Let’s see for values assigned to dimnames.

**R code:**

`vector1 <- c(2,18,30)`

vector2 <- c(10,14,17,13,11,15,22,11,33)

column.names <- c("COL1","COL2","COL3","COL4")

row.names <- c("ROW1","ROW2","ROW3")

matrix.names <- c("Matrix1","Matrix2")

array(c(vector1,vector2),dim = c(3,4,2),dimnames = list(row.names,column.names,

matrix.names ))

**Output:**

Now we are good at creating an array of any dimensionality. Lets now focus on the way of accessing any element in an array.

### How to Create an Access Elements array in R?

Below are different access elements on how to create an array in r as follows –

#### Scenario 1:

Let’s say we have the same array in R:

**R Code:**

`vector1 <- c(2,18,30)`

vector2 <- c(10,14,17,13,11,15,22,11,33)

column.names <- c("COL1","COL2","COL3","COL4")

row.names <- c("ROW1","ROW2","ROW3")

matrix.names <- c("Matrix1","Matrix2")

result <- array(c(vector1,vector2),dim = c(3,4,2),dimnames = list(row.names,column.names,

matrix.names))

**Output:**

Now, we need to access 3^{rd} row,3^{rd} column of the second matric in the array.

**R Code:**

`vector1 <- c(2,18,30)`

vector2 <- c(10,14,17,13,11,15,22,11,33)

column.names <- c("COL1","COL2","COL3","COL4")

row.names <- c("ROW1","ROW2","ROW3")

matrix.names <- c("Matrix1","Matrix2")

result <- array(c(vector1,vector2),dim = c(3,4,2),dimnames = list(row.names,column.names,

matrix.names))

result[3,3,2]

**Output:**

To summarize this, square brackets are used to denote an index. To specify the index in arrays, there are four choices available: positive integers, negative integers, logical values, element names

#### Scenario 2:

One needs to access an entire 1st array matrix:

**R Code:**

`vector1 <- c(2,18,30)`

vector2 <- c(10,14,17,13,11,15,22,11,33)

column.names <- c("COL1","COL2","COL3","COL4")

row.names <- c("ROW1","ROW2","ROW3")

matrix.names <- c("Matrix1","Matrix2")

result <- array(c(vector1,vector2),dim = c(3,4,2),dimnames = list(row.names,column.names,

matrix.names))

result[,,1]

**Output:**

### Different Array Operation With Examples

This section will provide you grip over various operations carried out on arrays for achieving various results.

#### 1. Addition & Subtraction:

Multidimensional matrix has to be converted to the one-dimensional matrix, in order to be added or subtracted.

**Addition:**

R code:

`vector1 <- c(2,18,30)`

vector2 <- c(10,14,17,13,11,15,22,11,33)

column.names <- c("COL1","COL2","COL3","COL4")

row.names <- c("ROW1","ROW2","ROW3")

matrix.names <- c("Matrix1","Matrix2")

result <- array(c(vector1,vector2),dim = c(3,4,2),dimnames = list(row.names,column.names,

matrix.names))

result[,,1]
result[,,2]
print(result[,,1] + result[,,2])

**Output:**

**Subtraction:**

**R code:**

`vector1 <- c(2,18,30)`

vector2 <- c(10,14,17,13,11,15,22,11,33)

column.names <- c("COL1","COL2","COL3","COL4")

row.names <- c("ROW1","ROW2","ROW3")

matrix.names <- c("Matrix1","Matrix2")

result <- array(c(vector1,vector2),dim = c(3,4,2),dimnames = list(row.names,column.names,

matrix.names))

result[,,1]
result[,,2]
print(result[,,1] - result[,,2])

Output:

#### 2. Calculations on Array element

A function name apply(), helps in applying any operation across array elements.

**Syntax: **

`apply(x, margin, fun)`

Here x is an array, the margin here refers to either rows or columns.

- MARGIN=1 for row-wise operation
- MARGIN=2 for column-wise operation
- MARGIN=c(1,2) for both.

Fun is the function applied across elements in the array of the data frame. This could be the standard functions which are part of R or custom functions (user-defined)

**Example 1:**

Row Wise R Code:

`vector1 <- c(2,18,30)`

vector2 <- c(10,14,17,13,11,15,22,11,33)

column.names <- c("COL1","COL2","COL3","COL4")

row.names <- c("ROW1","ROW2","ROW3")

matrix.names <- c("Matrix1","Matrix2")

result <- array(c(vector1,vector2),dim = c(3,4,2),dimnames = list(row.names,column.names,

matrix.names))

result[,,1]
result[,,2]
apply(result[,,1],1,sum)

##### Output:

**Column Wise – R Code:**

`vector1 <- c(2,18,30)`

vector2 <- c(10,14,17,13,11,15,22,11,33)

column.names <- c("COL1","COL2","COL3","COL4")

row.names <- c("ROW1","ROW2","ROW3")

matrix.names <- c("Matrix1","Matrix2")

result <- array(c(vector1,vector2),dim = c(3,4,2),dimnames = list(row.names,column.names,

matrix.names))

result[,,1]
result[,,2]
apply(result[,,1],2,sum)

##### Output:

This gives output in vector form which contains sum of individual columns. Here “sum” is standard R function.

**Example 2:**

R Code:

`vector1 <- c(2,18,30)`

vector2 <- c(10,14,17,13,11,15,22,11,33)

column.names <- c("COL1","COL2","COL3","COL4")

row.names <- c("ROW1","ROW2","ROW3")

matrix.names <- c("Matrix1","Matrix2")

result <- array(c(vector1,vector2),dim = c(3,4,2),dimnames = list(row.names,column.names,

matrix.names))

result[,,1]
result[,,2]
apply(result[,,1],1,function(x) x+10)

##### Output:

This gives the output of the same dimension. The thing to notice here is, we have applied user-defined function. This function is very useful and powerful while solving real-world problems. The function applied is also base for other complex functions like lapply(), rapply(), etc.

#### 3. Check for Array

Check for array if the object is an array or not. The function name is.array() is a primitive function that lets you do so. Its gives output in terms True or False

**R Code:**

`vector1 <- c(2,18,30)`

vector2 <- c(10,14,17,13,11,15,22,11,33)

column.names <- c("COL1","COL2","COL3","COL4")

row.names <- c("ROW1","ROW2","ROW3")

matrix.names <- c("Matrix1","Matrix2")

result <- array(c(vector1,vector2),dim = c(3,4,2),dimnames = list(row.names,column.names,

matrix.names))

result[,,1]
result[,,2]
is.array(result)

**Output:**

#### 4. Check size of Array

Knowing dimensionality, a number of rows, columns of array helps in slicing and dicing of data. Here are some functions to do that: dim, nrow, ncol

**R code:**

`vector1 <- c(2,18,30)`

vector2 <- c(10,14,17,13,11,15,22,11,33)

result <- array(c(vector1,vector2),dim = c(3,4,2))

print(result)

dim(result)

nrow(result)

ncol(result)

**Output:**

#### 5. Check names of row and columns

In order to know the names of rows, columns and dimension names of an array. Below are the shown implementation of it.

**R code:**

`vector1 <- c(2,18,30)`

vector2 <- c(10,14,17,13,11,15,22,11,33)

column.names <- c("COL1","COL2","COL3","COL4")

row.names <- c("ROW1","ROW2","ROW3")

matrix.names <- c("Matrix1","Matrix2")

result <- array(c(vector1,vector2),dim = c(3,4,2),dimnames = list(row.names,column.names,

matrix.names))

rownames(result)

colnames(result)

dimnames(result)

**Output:**

### Conclusion:

Going through the above content would have given you a clear understanding of arrays in R. R is a statistical language, and arrays are frequently used data objects. This means, working with varieties of operations like add, subtract, apply, etc. with an array in any application will now be a cake walk for you.

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