What is the function of the WHERE statement in a DATA step?

The WHERE statement in a DATA step is specifically utilized to filter observations based on specified conditions. This means that when you add a WHERE statement to your DATA step, SAS will only include the observations in the output dataset that meet the criteria specified in that statement.

For instance, if you want to create a new dataset that contains only the records for a certain year or those that meet a particular condition (such as age being greater than 30), the WHERE statement allows you to apply this filter directly within the DATA step, thereby preventing unwanted observations from being included in your final result. This functionality is crucial for data management, as it helps in narrowing down datasets to only the relevant records needed for analysis or reporting.

In contrast, defining a new variable pertains to using assignment statements within the DATA step, while merging datasets typically involves procedures such as PROC MERGE. Sorting data is accomplished through the PROC SORT procedure, and not the WHERE statement. Thus, filtering observations with the WHERE statement is fundamental for efficiently handling and preparing datasets for further analysis.