8.11 Encoding Missingness

When a predictor is discrete in nature, missingness can be directly encoded into the predictor as if it were a naturally occurring category. This makes sense for structurally missing values such as the example of alleys in the Ames housing data. Here, it is sensible to change the missing values to a category of “no alley.” In other cases, the missing values could simply be encoded as “missing” or “unknown.”