Ifelse vectorized function in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of ifelse with numeric vector

What is the output of the following R code using ifelse?

R Programming

x <- c(2, 5, 8, 1)
result <- ifelse(x > 4, x * 2, x + 1)
print(result)

A [1] 3 10 16 2

B [1] 2 5 8 1

C [1] 3 5 8 2

D [1] 4 10 16 2

💡 Hint

Remember that ifelse applies the condition element-wise and returns a vector.

The condition x > 4 is checked for each element: for 2 and 1 it is FALSE, so we add 1; for 5 and 8 it is TRUE, so we multiply by 2.

🧠 Conceptual

intermediate

Understanding ifelse with NA values

What will be the output of this R code using ifelse with NA values?

R Programming

x <- c(NA, 3, 7, NA)
result <- ifelse(is.na(x), 0, x)
print(result)

A [1] 0 3 7 0

B [1] NA 3 7 NA

C [1] 0 NA NA 0

D [1] 0 0 0 0

💡 Hint

Check how is.na(x) returns TRUE or FALSE for each element.

The is.na(x) returns TRUE for NA elements, so ifelse replaces those with 0, and keeps other values as is.

🔧 Debug

advanced

Identify the error in ifelse usage

What error does the following R code produce?

R Programming

x <- c(1, 2, 3)
result <- ifelse(x > 2, "High", 0)
print(result)

A Error: non-numeric argument to binary operator

B Warning: Incompatible types in ifelse condition

C No error; output is [1] "0" "0" "High"

D No error; output is [1] 0 0 "High"

💡 Hint

Check how R handles mixed types in ifelse output vectors.

R coerces numeric 0 to character "0" because the other output is a character string. So no error occurs, and output is character vector.

📝 Syntax

advanced

Syntax error in ifelse usage

Which option contains a syntax error in using ifelse in R?

A ifelse(x > 0, "Positive", "Negative")

B ifelse(x > 0 "Positive", "Negative")

C )"evitageN" ,"evitisoP" ,0 > x(eslefi

D felse(x > 0, "Positive", "Negative")

💡 Hint

Look for missing commas or parentheses.

Option B is missing a comma between the condition and the true value, causing a syntax error.

🚀 Application

expert

Using ifelse to categorize numeric vector

Given scores <- c(45, 67, 89, 55, 72), which code correctly assigns grades: "Fail" for scores below 50, "Pass" for 50 to 75, and "Distinction" for above 75?

R Programming

scores <- c(45, 67, 89, 55, 72)

A grades <- ifelse(scores < 50, "Fail", ifelse(scores >= 75, "Pass", "Distinction"))

B grades <- ifelse(scores < 50, "Fail", ifelse(scores > 75, "Distinction", "Pass"))

C grades <- ifelse(scores <= 50, "Fail", ifelse(scores < 75, "Pass", "Distinction"))

D grades <- ifelse(scores < 50, "Fail", ifelse(scores <= 75, "Pass", "Distinction"))

💡 Hint

Think about the order of conditions and inclusive ranges.

Option D correctly nests ifelse to assign "Fail" if below 50, then "Pass" if 50 to 75 inclusive, else "Distinction".