R Factors
Factors
Factors are used to categorize data. Examples of factors are:
- Demography: Male/Female
- Music: Rock, Pop, Classic, Jazz
- Training: Strength, Stamina
To create a factor, use the factor() function
and add a vector as argument:
Example
# Create a factor
music_genre <- factor(c("Jazz", "Rock", "Classic", "Classic", "Pop", "Jazz",
"Rock", "Jazz"))
# Print the factor
music_genre
Result:
[1] Jazz Rock Classic Classic Pop Jazz Rock Jazz Levels: Classic Jazz Pop Rock
You can see from the example above that that the factor has four levels (categories): Classic, Jazz, Pop and Rock.
To only print the levels, use the levels() function:
Example
music_genre <- factor(c("Jazz", "Rock", "Classic", "Classic", "Pop", "Jazz",
"Rock", "Jazz"))
levels(music_genre)
Result:
[1] "Classic" "Jazz" "Pop" "Rock"
You can also set the levels, by adding the levels argument inside the
factor() function:
Example
music_genre <- factor(c("Jazz", "Rock", "Classic", "Classic", "Pop", "Jazz",
"Rock", "Jazz"), levels = c("Classic", "Jazz", "Pop", "Rock", "Other"))
levels(music_genre)
Result:
[1] "Classic" "Jazz" "Pop" "Rock" "Other"
Factor Length
Use the length() function to find out how many items there are in the factor:
Example
music_genre <- factor(c("Jazz", "Rock", "Classic", "Classic", "Pop", "Jazz",
"Rock", "Jazz"))
length(music_genre)
Result:
[1] 8
Access Factors
To access the items in a factor, refer to the index number, using [] brackets:
Example
Access the third item:
music_genre <- factor(c("Jazz", "Rock", "Classic", "Classic", "Pop", "Jazz",
"Rock", "Jazz"))
music_genre[3]
Result:
[1] Classic Levels: Classic Jazz Pop Rock
Change Item Value
To change the value of a specific item, refer to the index number:
Example
Change the value of the third item:
music_genre <- factor(c("Jazz", "Rock", "Classic", "Classic", "Pop", "Jazz",
"Rock", "Jazz"))
music_genre[3] <- "Pop"
music_genre[3]
Result:
[1] Pop Levels: Classic Jazz Pop Rock
Note that you cannot change the value of a specific item if it is not already specified in the factor. The following example will produce an error:
Example
Trying to change the value of the third item ("Classic") to an item that does not exist/not predefined ("Opera"):
music_genre <- factor(c("Jazz", "Rock", "Classic", "Classic", "Pop", "Jazz",
"Rock", "Jazz"))
music_genre[3] <- "Opera"
music_genre[3]
Result:
Warning message: In `[<-.factor`(`*tmp*`, 3, value = "Opera") : invalid factor level, NA generated
However, if you have already specified it inside the levels argument, it will work:
Example
Change the value of the third item:
music_genre <- factor(c("Jazz", "Rock", "Classic", "Classic", "Pop", "Jazz",
"Rock", "Jazz"), levels = c("Classic", "Jazz", "Pop", "Rock",
"Opera"))
music_genre[3] <- "Opera"
music_genre[3]
Result:
[1] Opera Levels: Classic Jazz Pop Rock Opera
