Anonymous functions in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of an anonymous function with lapply

What is the output of this R code using an anonymous function with lapply?

R Programming

result <- lapply(1:3, function(x) x^2)
print(result)

A list(1, 4, 9)

B c(1, 4, 9)

C c(1, 2, 3)

D list(1, 2, 3)

💡 Hint

Remember that lapply returns a list, not a vector.

The anonymous function squares each number from 1 to 3. lapply returns a list of these squared values: 1, 4, and 9.

❓ Predict Output

intermediate

Output of anonymous function with sapply

What is the output of this R code using an anonymous function with sapply?

R Programming

result <- sapply(1:4, function(x) if (x %% 2 == 0) x else NA)
print(result)

A 1 2 3 4

B NA NA NA NA

C 2 4

D NA 2 NA 4

💡 Hint

Check how the anonymous function returns values for even and odd numbers.

The function returns the number if it is even, otherwise NA. sapply simplifies the result to a vector: NA 2 NA 4.

🔧 Debug

advanced

Identify the error in anonymous function usage

What error does this R code produce when run?

R Programming

result <- lapply(1:3, function(x) {x * 2
})
print(result)

A No error, prints list(2, 4, 6)

B NULL values in the list

C SyntaxError: unexpected end of input

D Error: object 'x' not found

💡 Hint

Check if the function body returns a value correctly.

The function multiplies each number by 2 and returns it. The code runs without error and prints list(2, 4, 6).

❓ Predict Output

advanced

Output of nested anonymous functions

What is the output of this R code with nested anonymous functions?

R Programming

outer_func <- function(f) {
  f(5)
}
result <- outer_func(function(x) x * x)
print(result)

A function(x) x * x

B 5

C 25

D Error: argument is not a function

💡 Hint

The outer function calls the anonymous function with 5.

The anonymous function squares its input. Called with 5, it returns 25.

🧠 Conceptual

expert

Understanding environment capture in anonymous functions

Consider this R code. What is the value of result after running it?

R Programming

make_funcs <- function() {
  funcs <- list()
  for (i in 1:3) {
    funcs[[i]] <- function() i
  }
  funcs
}
funcs <- make_funcs()
result <- sapply(funcs, function(f) f())

A 1 2 3

B 3 3 3

C Error: object 'i' not found

D 1 1 1

💡 Hint

Think about how R captures the variable i in the anonymous functions inside the loop.

All functions capture the same variable i, which after the loop ends is 3. So all return 3.