R Nested Functions

R Nested Functions

Nested functions in R mean defining a function inside another function.

The inner function is only accessible within the outer function.

This concept is closely related to scope and lexical scoping in R.

1. What is a Nested Function?

A function written inside another function
Inner function can use variables of the outer function
Improves encapsulation and code organization

2. Basic Nested Function Example

Output:

Explanation:

outer() takes argument x
Inside it, inner() is defined
inner() squares its argument (y * y)
outer() calls inner(x)
outer(5) → inner(5) → 5 * 5 → 25

3. Accessing Outer Function Variables

Output:

Explanation:

outer(5) → so x = 5
inner(10) is called → so y = 10
Inside inner() → x + y → 5 + 10
Result = 15

4. Nested Function with Multiple Operations

calculator <- function(a, b) {
  
  add <- function() a + b
  subtract <- function() a - b
  multiply <- function() a * b
  divide <- function() a / b
  
  list(
    sum = add(),
    difference = subtract(),
    product = multiply(),
    quotient = divide()
  )
}

calculator(4, 5)

calculator <- function(a, b) {

add <- function() a + b

subtract <- function() a - b

multiply <- function() a * b

divide <- function() a / b

list(

sum = add(),

difference = subtract(),

product = multiply(),

quotient = divide()

)

}

calculator(4, 5)

Output:

$sum

[1] 9

$difference

[1] –1

$product

[1] 20

$quotient

[1] 0.8

Explanation:

add() → 4 + 5 = 9
subtract() → 4 – 5 = -1
multiply() → 4 × 5 = 20
divide() → 4 ÷ 5 = 0.8

5. Why Use Nested Functions?

Hide helper logic
Avoid global namespace pollution
Improve readability
Maintain logical grouping of code

6. Scope Rules in Nested Functions

Output:

Inner x does not change outer x

7. Using `<<-` in Nested Functions (Advanced)

Output:

<<- modifies the outer variable
Use carefully

8. Returning a Nested Function (Closure)

power_fn <- function(n) {
  function(x) {
    x ^ n
  }
}

square <- power_fn(2)
cube <- power_fn(3)

square(4)
cube(4)

power_fn <- function(n) {

function(x) {

x ^ n

}

square <- power_fn(2)

cube <- power_fn(3)

square(4)

cube(4)

Output:

[1] 16

[1] 64

Explanation:

power_fn(n) returns a function
That returned function calculates x ^ n
square <- power_fn(2) → creates a function for power 2
cube <- power_fn(3) → creates a function for power 3
square(4) → 4² = 16
cube(4) → 4³ = 64

This is a perfect example of closure in R (function returning another function).

Nested Functions vs Normal Functions

Feature	Nested Function	Normal Function
Scope	Local	Global
Accessibility	Inside parent only	Anywhere
Use case	Helper logic	Reusable logic

Summary

Nested functions are functions inside functions
Inner function can access outer variables
Helps in code organization and safety
Supports closures and functional programming

R Nested Functions