What is one primary use of the SET statement in a DATA step?

The SET statement in a DATA step is specifically designed to bring data from existing datasets into the data step for processing. By utilizing the SET statement, you can read observations from one or more SAS datasets sequentially into the program's data step data set. This allows you to manipulate, analyze, or otherwise process the data as needed.

When the SET statement is used, each observation from the specified dataset is read into the program's data step one at a time, allowing you to perform operations such as computations, transformations, or data aggregations. This functionality is essential for tasks that involve combining, modifying, or creating new datasets based on pre-existing data.

Other choices discuss functionalities that the SET statement does not perform. Defining new formats is related to using a FORMAT statement, reading data from an external file involves using the INFILE statement, and filtering records based on conditions typically requires the use of the WHERE statement or conditional logic within the DATA step. Thus, the distinct role of the SET statement is to facilitate the retrieval of data from existing datasets.