Negative indexing for exclusion in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of negative indexing to exclude elements

What is the output of the following R code?

R Programming

x <- c(10, 20, 30, 40, 50)
result <- x[-c(2, 4)]
print(result)

A [1] 10 20 30 40 50

B [1] 20 40

C [1] 10 30 40 50

D [1] 10 30 50

💡 Hint

Negative indexing in R removes the elements at the specified positions.

Using negative indices in R excludes those elements from the vector. Here, positions 2 and 4 (values 20 and 40) are removed, leaving 10, 30, and 50.

❓ Predict Output

intermediate

Negative indexing with single element exclusion

What will be printed by this R code?

R Programming

y <- c('a', 'b', 'c', 'd')
print(y[-3])

A [1] "c"

B [1] "a" "b" "d"

C [1] "a" "b" "c" "d"

D [1] "a" "c" "d"

💡 Hint

Negative indexing removes the element at the given position.

The element at position 3 ('c') is excluded, so the output is 'a', 'b', and 'd'.

🔧 Debug

advanced

Identify the error in negative indexing usage

What error does this R code produce?

R Programming

z <- c(5, 10, 15, 20)
print(z[-c(2, -3)])

A Error: only 0's may be mixed with negative subscripts

B [1] 5 15 20

C [1] 5 10 20

D Error: invalid subscript type 'list'

💡 Hint

Negative and positive indices cannot be mixed in the same subscript.

In R, you cannot mix negative and positive indices in the same vector for subsetting. Here, -3 is negative but inside c(2, -3) mixes positive 2 and negative -3, causing an error.

🧠 Conceptual

advanced

Length of vector after negative indexing exclusion

Given the vector v <- 1:8, what is the length of v[-c(1, 3, 5)]?

A 5

B 6

C 8

D 3

💡 Hint

Negative indexing removes the specified elements from the vector.

Removing elements at positions 1, 3, and 5 from an 8-element vector leaves 5 elements.

❓ Predict Output

expert

Output of negative indexing with repeated indices

What is the output of this R code?

R Programming

w <- c(2, 4, 6, 8, 10)
print(w[-c(2, 2, 4)])

A [1] 2 6 8 10

B [1] 4 8

C [1] 2 6 10

D Error: invalid subscript type 'double'

💡 Hint

Repeated indices in negative indexing exclude the element only once.

Positions 2 and 4 are excluded. Repeating 2 does not cause error or exclude more elements. Remaining elements are at positions 1, 3, and 5: 2, 6, 10.