A Factor is a data structure that is used to work with categorizable datas.

Suppose a data field such as marital status may contain only values from single, married, separated, divorced, or widowed.

In such a case, we know the possible values beforehand and these predefined, distinct values are called levels of a factor.

Create a Factor in R

In R, we use the factor() function to create a factor. Once a factor is created, it can only contain predefined set values called levels.

The syntax for creating a factor is

factor(vector)

Here, factor() takes a vector as an argument.

Let's see an example,

# create a factor
students_gender <- factor(c("male", "female", "male", "transgender", "female"))

# print the marital_status factor
print(students_gender)

Output

[1] male   female   male   transgender    female     
Levels: female male transgender

In the above example, we have used the factor() function to create the factor named students_gender.

Notice while printing students_gender, we get two outputs

• All the vectors items
• predefined possible values we know beforehand i.e. levels of students_gender

Access Factors Elements

Accessing vector elements is similar to that of vectors. We use the index number. For example,

# create a factor
students_gender <- factor(c("male", "female", "male", "transgender", "female"))

# access 1st element of students_gender
print(students_gender[1])

# access 4th element of students_gender
print(students_gender[4])

Output

[1] male
Levels: female male transgender
[1] transgender
Levels: female male transgender

In the above example, we have used the index number to access elements of the students_gender

• students_gender[1] - returns the 1st element of students_gender i.e "male"
• students_gender[4] - returns the 4th element of students_gender i.e. "transgender"

Note that each time we access and print factor elements we get a level of factor too.

Modify Factor Element

To change a vector element, we can simply reassign a new value to the specific index. For example,

# create a factor
marital_status <- factor(c("married", "single", "single", "divorced", "married"))

# print the marital_status factor
marital_status[1] <- "divorced"

print(marital_status[1])

Output

[1] divorced
Levels: divorced married single

Here, we have reassigned a new value to index 1 of the marital_status factor to change the element from "married" to "divorced".

# create a factor
marital_status <- factor(c("married", "single", "single", "divorced", "married"))

cat("Total Elements:", length(marital_status))

Total Elements: 5

# create a factor
marital_status <- factor(c("married", "single", "single", "divorced", "married"))

# iterate through each elements of marital_status
for (status in marital_status) {
    print(status)
}

[1] "married"
[1] "single"
[1] "single"
[1] "divorced"
[1] "married"