List to vector conversion in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of unlist on nested list

What is the output of the following R code?

R Programming

my_list <- list(a = 1:3, b = list(4, 5))
result <- unlist(my_list)
print(result)

A

a1 a2 a3 b1 b2
1  2  3  4  5

B 1 2 3 4 5

C list(1, 2, 3, 4, 5)

D Error: cannot unlist nested lists

💡 Hint

Remember that unlist flattens nested lists and preserves names.

The unlist function converts the nested list into a named vector, flattening all elements and preserving the names from the original list.

❓ Predict Output

intermediate

Result of as.vector on a list

What is the output of this R code?

R Programming

my_list <- list(10, 20, 30)
result <- as.vector(my_list)
print(result)

A [1] list(10, 20, 30)

B Error: cannot convert list to vector

C [[1]] 10 [[2]] 20 [[3]] 30

D [1] 10 20 30

💡 Hint

as.vector tries to simplify the list to a vector if possible.

as.vector returns the list unchanged because the list elements are not simplified to an atomic vector.

🔧 Debug

advanced

Why does this unlist produce unexpected output?

Consider this code snippet: my_list <- list(c(1, 2), c('a', 'b')) result <- unlist(my_list) print(result) Why does the output contain characters instead of numbers?

R Programming

my_list <- list(c(1, 2), c('a', 'b'))
result <- unlist(my_list)
print(result)

A Because the list contains mixed types, unlist throws an error.

B Because unlist converts all elements to the most flexible type, here character, to hold all values.

C Because unlist only works on numeric lists and fails silently.

D Because unlist converts all elements to numeric, but characters cause NA.

💡 Hint

Think about how R handles vectors with mixed types.

When unlist encounters mixed types, it coerces all elements to a common type that can hold all values, which is character in this case.

🧠 Conceptual

advanced

Length of vector after unlist

If you have a list like this: list(1:3, 4:6, 7:9), what is the length of the vector after applying unlist()?

R Programming

my_list <- list(1:3, 4:6, 7:9)
result <- unlist(my_list)
length(result)

A 9

B 3

C 1

D Error: length undefined

💡 Hint

Count all elements inside all sublists combined.

unlist flattens the list into a single vector containing all elements, so length is the total number of elements.

📝 Syntax

expert

Which code produces a numeric vector from a list of numeric vectors?

Given a list of numeric vectors, which R code correctly converts it into a single numeric vector?

R Programming

my_list <- list(c(1,2), c(3,4), c(5,6))

A result <- vector(my_list)

B result <- as.vector(my_list)

C result <- c(my_list)

D result <- unlist(my_list)

💡 Hint

Check which function flattens nested lists properly.

unlist flattens the list into a single vector. as.vector returns the list unchanged, c() concatenates but keeps list structure, vector() creates an empty vector.