Nested lists in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested list indexing

What is the output of the following R code?

R Programming

nested_list <- list(a = list(1, 2, 3), b = list(4, 5, 6))
result <- nested_list$a[[2]]
print(result)

A [1] 3

B [1] 2

C [1] 1

D NULL

💡 Hint

Remember that [[ ]] extracts the element itself, not a sublist.

nested_list$a is a list of three elements: 1, 2, 3. Using [[2]] extracts the second element, which is 2.

❓ Predict Output

intermediate

Length of nested list element

What is the value of length(nested_list$b) after running this code?

R Programming

nested_list <- list(a = list(1, 2, 3), b = list(4, 5, 6))
length(nested_list$b)

A 3

B 1

C 6

D NULL

💡 Hint

length() returns the number of elements in the list, not the sum of elements.

nested_list$b is a list with three elements: 4, 5, and 6, so length is 3.

❓ Predict Output

advanced

Output of nested list modification

What is the output of this R code?

R Programming

nested_list <- list(a = list(1, 2), b = list(3, 4))
nested_list$a[[2]] <- 10
print(nested_list$a)

A Error: object of type 'closure' is not subsettable

B

[[1]] 1
[[2]] 2

C [1] 1 10

D

[[1]] 1
[[2]] 10

💡 Hint

Using [[ ]] allows you to replace the element inside the nested list.

The second element of nested_list$a is replaced by 10. Printing nested_list$a shows the list with elements 1 and 10.

❓ Predict Output

advanced

Accessing deeply nested list element

What is the output of this code?

R Programming

nested_list <- list(x = list(y = list(z = 42)))
print(nested_list$x$y$z)

A [1] 42

B NULL

C Error: object 'z' not found

D [1] "42"

💡 Hint

Use $ to access named elements inside nested lists.

nested_list$x$y$z accesses the value 42 stored deeply inside the nested list.

🧠 Conceptual

expert

Number of elements in a nested list

Given the nested list below, how many top-level elements does it have?

R Programming

nested_list <- list(alpha = list(1, 2), beta = list(3, 4), gamma = 5)

A 5

B 2

C 3

D 1

💡 Hint

Count only the elements directly inside nested_list, not inside sublists.

nested_list has three top-level elements named alpha, beta, and gamma.