Variable scope (lexical scoping) in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested function with lexical scope

What is the output of this R code?

R Programming

x <- 10
f <- function() {
  x <- 20
  g <- function() {
    x
  }
  g()
}
f()

A [1] 20

B [1] 10

C Error: object 'x' not found

D [1] NULL

💡 Hint

Remember that inner functions use variables from their defining environment unless shadowed.

The inner function g() uses the x defined in f(), which is 20, not the global x which is 10.

❓ Predict Output

intermediate

Value of variable after function call

What is the value of x after running this code?

R Programming

x <- 5
foo <- function() {
  x <- 10
}
foo()
x

A [1] 10

B [1] 5

C NULL

D Error: object 'x' not found

💡 Hint

Does the function foo() change the global x or only a local copy?

The assignment inside foo() creates a local x; the global x remains unchanged at 5.

❓ Predict Output

advanced

Output of function modifying global variable with <<-

What is the output of this code?

R Programming

x <- 1
modify <- function() {
  x <<- 2
}
modify()
x

A NULL

B [1] 1

C Error: object 'x' not found

D [1] 2

💡 Hint

The <<- operator assigns to a variable in the parent environment.

The <<- operator changes the global x to 2, so the output is 2.

❓ Predict Output

advanced

Error caused by variable scope in nested functions

What error does this code produce?

R Programming

outer <- function() {
  inner <- function() {
    y
  }
  inner()
}
outer()

A Error: object 'y' not found

B NULL

C [1] 0

D [1] NA

💡 Hint

Is y defined anywhere in the function or global environment?

The variable y is not defined anywhere accessible, so R raises an error.

🧠 Conceptual

expert

How many variables are in the environment after execution?

Consider this code. How many variables are in the environment of function f after it runs?

R Programming

f <- function() {
  a <- 1
  b <- 2
  g <- function() {
    c <- 3
    a + b + c
  }
  g()
}

A 4 variables: a, b, c, and g

B 3 variables: a, b, and c

C 2 variables: a and b

D 1 variable: g

💡 Hint

Variables inside g() exist only during g() execution, not in f()'s environment after g() finishes.

Inside f(), only a and b exist as variables after g() runs; c is local to g() and does not remain in f().