Vector indexing (1-based) in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this R code using 1-based indexing?

Consider the vector v <- c(10, 20, 30, 40, 50). What is the output of v[3]?

R Programming

v <- c(10, 20, 30, 40, 50)
v[3]

A [1] 30

B [1] 20

C [1] 40

D [1] 10

💡 Hint

Remember R vectors start counting at 1, not 0.

In R, vector indexing starts at 1, so v[3] returns the third element, which is 30.

❓ Predict Output

intermediate

What does this R code output when indexing with a vector?

Given v <- c(5, 10, 15, 20, 25), what is the output of v[c(2, 4)]?

R Programming

v <- c(5, 10, 15, 20, 25)
v[c(2, 4)]

A [1] 10 20

B [1] 5 15

C [1] 15 25

D [1] 20 25

💡 Hint

Indexing with a vector returns elements at those positions.

v[c(2,4)] returns the elements at positions 2 and 4, which are 10 and 20.

🧠 Conceptual

advanced

What error does this R code raise when indexing with zero?

What happens when you run v <- c(1,2,3); v[0] in R?

R Programming

v <- c(1,2,3)
v[0]

A Throws an error: subscript out of bounds

B Returns the first element of v

C Returns an empty vector with no elements

D Returns NULL

💡 Hint

In R, zero is a special index that means no elements.

Indexing with 0 returns an empty vector of the same type, no error is raised.

❓ Predict Output

advanced

What is the output of negative indexing in R?

Given v <- c(2, 4, 6, 8, 10), what does v[-c(1,3)] return?

R Programming

v <- c(2, 4, 6, 8, 10)
v[-c(1,3)]

A [1] 2 6 8 10

B [1] 4 8 10

C [1] 2 4 6

D [1] 4 6 8 10

💡 Hint

Negative indices exclude those positions from the result.

v[-c(1,3)] excludes elements at positions 1 and 3, returning elements at positions 2,4,5.

❓ Predict Output

expert

What is the output of this complex vector indexing in R?

Given v <- c(3, 6, 9, 12, 15), what is the output of v[c(TRUE, FALSE, TRUE, FALSE, TRUE)]?

R Programming

v <- c(3, 6, 9, 12, 15)
v[c(TRUE, FALSE, TRUE, FALSE, TRUE)]

A [1] 6 12

B [1] 15

C [1] 3 6 9

D [1] 3 9 15

💡 Hint

Logical vectors select elements where TRUE appears.

The logical vector selects elements at positions 1,3,5 which are 3, 9, and 15.