What does the BY statement achieve in PROC SORT?

The BY statement in PROC SORT is used to sort the dataset based on multiple variables. When you specify multiple variables in the BY statement, SAS will first sort the data by the first variable listed, and then within the groups of that variable, it will sort by the second variable, and so on for any additional variables. This hierarchical sorting method creates a more organized dataset where records are grouped and ordered according to the specified variables.

In contrast, creating a new dataset is not the primary purpose of the BY statement; instead, it modifies the way the existing dataset is organized. Filtering the dataset isn’t achieved through the BY statement, as filtering involves selecting a subset of data based on specific conditions. Merging datasets is a different operation that typically involves the MERGE statement, which is distinct from sorting. Thus, the BY statement's functionality within PROC SORT is primarily to enable sorting by multiple variables.