Convert NA into Factor Level in R (Example) | addNA Function for Missing Data

This article explains how to turn NA values into a new factor level using the addNA function in the R programming language.

Table of contents:

Let’s start right away!

Example Data

The following data will be used as basement for this R tutorial:

my_fac <- factor(c("a", "b", NA, "a", "c", NA))    # Create example factor
my_fac                                             # Print example factor
# [1] a    b    <NA> a    c    <NA>
# Levels: a b c

The previous output of the RStudio console shows the structure of our example data: We have created a factor vector with the three factor levels a, b, and c. Furthermore, our factor contains some NA values (i.e. missing data).

Example: Turn NA into Extra Factor Level Using addNA() Function

In this example, I’ll demonstrate how to convert NA values to a new factor level using the addNA function in R.

Consider the R code below:

my_fac_NA <- addNA(my_fac)                         # Apply addNA function
my_fac_NA                                          # Print updated factor
# [1] a    b    <NA> a    c    <NA>
# Levels: a b c <NA>

Have a look at the previous output: It shows NA as additional factor level.

Video, Further Resources & Summary

Would you like to learn more about the application of the addNA function? Then you may watch the following video on my YouTube channel. I illustrate the examples of this article in the video.

In addition, you may want to have a look at the related tutorials that I have published on this website. I have released numerous tutorials already:

• Convert Factor to Character Class
• na_if R Function of dplyr Package
• Convert Values in Column into Row Names of Data Frame
• Help – Warning: invalid factor level, NA generated
• Convert Factor to Dummy Indicator Variables for Every Level
• R Programming Overview

In this R programming tutorial you have learned how to apply the addNA function. If you have any additional questions, don’t hesitate to let me know in the comments section.