Factor levels in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this factor levels code?

Consider the following R code that creates a factor and then changes its levels. What will be the output of levels(f)?

R Programming

f <- factor(c("low", "medium", "high", "medium", "low"))
levels(f) <- c("low", "medium", "high", "very high")
levels(f)

A Error: number of levels differs from previous

B [1] "low" "medium" "high"

C [1] "low" "medium" "high" "very high" "extreme"

D [1] "low" "medium" "high" "very high"

💡 Hint

The number of new levels must match the number of original levels exactly.

The original factor has 3 levels: 'high', 'low', 'medium' (sorted alphabetically). Assigning 4 new levels causes an error because the number differs.

❓ Predict Output

intermediate

What is the output of this factor level drop code?

Given this R code, what will be the output of levels(f) after dropping unused levels?

R Programming

f <- factor(c("apple", "banana", "apple", "cherry"), levels = c("apple", "banana", "cherry", "date"))
f <- droplevels(f[f != "date"])
levels(f)

A [1] "apple" "banana" "cherry" "date"

B Error: object 'f' not found

C [1] "apple" "banana"

D [1] "apple" "banana" "cherry"

💡 Hint

droplevels removes levels not present in the data.

The original factor has 4 levels but 'date' is not present in the data. After subsetting and dropping levels, 'date' is removed.

🔧 Debug

advanced

Why does this factor level assignment cause an error?

Examine the code below. Why does assigning new levels cause an error?

R Programming

f <- factor(c("a", "b", "c"))
levels(f) <- c("x", "y")

A Because the new levels vector contains invalid characters

B Because factor levels cannot be changed once created

C Because the new levels vector has fewer elements than the original levels

D Because the factor vector contains NA values

💡 Hint

The number of new levels must match the number of original levels.

The original factor has 3 levels but the new levels vector has only 2 elements, causing an error.

❓ Predict Output

advanced

What is the output of this factor releveling code?

What will be the output of levels(f) after running this code?

R Programming

f <- factor(c("small", "medium", "large"), ordered = TRUE)
f <- relevel(f, ref = "large")
levels(f)

A [1] "small" "medium" "large"

B [1] "large" "small" "medium"

C [1] "medium" "small" "large"

D Error: object 'relevel' not found

💡 Hint

relevel moves the specified level to the front.

The relevel function moves the reference level to the first position in the levels vector.

🧠 Conceptual

expert

How many levels does this factor have after modification?

Given the code below, how many levels does the factor f have after execution?

R Programming

f <- factor(c("red", "green", "blue", "green"), levels = c("red", "green", "blue", "yellow"))
f <- f[f != "yellow"]
f <- droplevels(f)
length(levels(f))

A 3

B 4

C 2

D 1

💡 Hint

droplevels removes unused levels after subsetting.

The original factor has 4 levels but 'yellow' is not present in the data after subsetting, so droplevels removes it, leaving 3 levels.