Factor creation in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a factor in R?

A factor in R is a data structure used to represent categorical data. It stores the data as integer codes with corresponding labels called levels.

beginner

How do you create a factor from a character vector in R?

Use the function factor() and pass the character vector as an argument. For example: factor(c("apple", "banana", "apple")).

intermediate

What does the levels argument do in factor()?

The levels argument sets the possible categories (levels) of the factor. It controls the order and which categories are included, even if not present in the data.

beginner

How can you check the levels of a factor in R?

Use the levels() function on the factor variable. It returns a character vector of the factor's levels.

intermediate

What happens if you create a factor with numeric values?

R treats the numeric values as categories, not numbers. The factor stores them as levels, so arithmetic operations won't work directly on factors.

Which function is used to create a factor in R?

A factor()

B as.factor()

C levels()

D categorize()

The factor() function creates a factor from a vector.

What does the levels argument in factor() control?

A The order and categories of the factor

B The numeric values of the factor

C The length of the vector

D The data type of the vector

The levels argument sets which categories exist and their order.

If you create a factor from the vector c("red", "blue", "red"), how many levels will it have?

A 1

B 3

C 2

D 0

There are two unique categories: "red" and "blue".

What will levels(factor(c(1, 2, 1))) return?

A An error

B [1, 2]

C ["1", "2", "3"]

D ["1", "2"]

Levels are stored as character strings representing the unique values.

Can you perform arithmetic directly on factors?

A Yes, factors behave like numbers

B No, factors represent categories, not numbers

C Only if levels are numeric

D Only with the <code>levels</code> argument

Factors represent categories, so arithmetic operations do not work directly.

Explain how to create a factor in R and why factors are useful.

Think about how R stores categories and why that helps with data analysis.

Describe what happens when you create a factor from numeric values and how it differs from numeric vectors.

Consider how factors treat numbers as labels, not quantities.