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:

[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:

[1] "Classic" "Jazz"    "Pop"     "Rock"   

You can also set the levels, by adding the levels argument inside the factor() function:

[1] "Classic" "Jazz"    "Pop"     "Rock"    "Other"

Factor Length

Use the length() function to find out how many items there are in the factor:

[1] 8

Access Factors

To access the items in a factor, refer to the index number, using [] brackets:

[1] Classic
Levels: Classic Jazz Pop Rock

Change Item Value

To change the value of a specific item, refer to the index number:

[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:

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:

[1] Opera
Levels: Classic Jazz Pop Rock Opera