What variable types can be created in the BY group when sorting data for further analysis in the DATA step?

In the context of sorting data for further analysis in a DATA step within SAS, the correct choice refers to the First. and Last. variable types. When data is processed in a BY group, SAS automatically creates temporary variables named First. and Last. for each variable in the BY statement. These variables are particularly useful for identifying the first and the last observation of each BY group.

When the dataset is sorted by the specified variables and processed in a DATA step, the First. variable takes the value of 1 (true) for the first observation of each new BY group and 0 (false) for all other observations. Conversely, the Last. variable takes the value of 1 for the last observation in each BY group and 0 for the rest. This facilitates operations such as summarizing data or performing calculations at the group level, as it allows programmers to easily distinguish between the beginning and ending of groups within the dataset.

Understanding how these special variables work enables you to perform more sophisticated data manipulations, such as calculating differences between groups or creating summary statistics without having to resort to additional sorting or complex programming constructs.