Factor creation in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of factor levels with default ordering

What is the output of the following R code?

f <- factor(c("apple", "banana", "apple", "cherry"))
levels(f)

R Programming

f <- factor(c("apple", "banana", "apple", "cherry"))
levels(f)

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

B [1] "banana" "apple" "cherry"

C [1] "apple" "cherry" "banana"

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

💡 Hint

Think about how R orders factor levels by default.

By default, R orders factor levels alphabetically. So the levels are "apple", "banana", "cherry".

❓ Predict Output

intermediate

Number of levels in a factor

What is the output of this R code?

f <- factor(c("red", "blue", "red", "green", "blue"))
length(levels(f))

R Programming

f <- factor(c("red", "blue", "red", "green", "blue"))
length(levels(f))

A 1

B 3

C 5

D 4

💡 Hint

Count unique values in the vector.

The factor has three unique values: "red", "blue", and "green", so the number of levels is 3.

❓ Predict Output

advanced

Effect of specifying levels in factor creation

What is the output of this R code?

f <- factor(c("small", "medium", "large", "medium"), levels = c("large", "medium", "small"))
levels(f)

R Programming

f <- factor(c("small", "medium", "large", "medium"), levels = c("large", "medium", "small"))
levels(f)

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

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

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

D [1] "large" "small" "medium"

💡 Hint

Levels are set explicitly in the factor function.

When levels are specified, R uses that order exactly for the factor levels.

❓ Predict Output

advanced

Output of factor with unused levels

What is the output of this R code?

f <- factor(c("cat", "dog"), levels = c("cat", "dog", "mouse"))
length(levels(f))

R Programming

f <- factor(c("cat", "dog"), levels = c("cat", "dog", "mouse"))
length(levels(f))

A 3

B 2

C 1

D 0

💡 Hint

Levels include all specified, even if not used in data.

The factor has three levels because "mouse" is included even though it does not appear in the data.

🧠 Conceptual

expert

Behavior of factor when converting numeric vector

Consider this R code:

v <- c(10, 20, 10, 30)
f <- factor(v)
levels(f)

What is the output of levels(f)?

R Programming

v <- c(10, 20, 10, 30)
f <- factor(v)
levels(f)

A [1] "1" "2" "3"

B [1] 10 20 30

C [1] "10" "20" "30"

D [1] 10 20 30 40

💡 Hint

Factor levels are always character strings representing unique values.

When a numeric vector is converted to a factor, levels are character strings of unique values sorted.