SAS 9.4 Language Reference, 6th Edition

Invoking BY-Group Processing

To create BY groups, you use the BY statement in one of two ways:

• DATA step

• PROC step (For information about BY-group processing with procedures, see

“Creating Titles That Contain BY-Group Information ” in Base SAS Procedures

Guide.)

The following DATA step program uses the SET statement to combine observations

from three SAS data sets by interleaving the files. The data is ordered by State City and

Zip.

data all_sales;

set region1 region2 region3;

by State City Zip;

… more SAS statements …

run;

Determining Whether the Data Requires

Preprocessing for BY-Group Processing

Before you perform BY-group processing on multiple data sets using the SET, MERGE,

and UPDATE statements, you must check the data to determine whether it requires

preprocessing. They require no preprocessing if the observations in all of the data sets

occur in one of the following patterns:

• ascending or descending numeric order

• ascending or descending character order

• not alphabetically or numerically ordered, but grouped in some way, such as by

calendar month or by a formatted value

If the observations are not in the order that you want, you must either sort the data set or

create an index for it before using BY-group processing.

If you use the MODIFY statement in BY-group processing, you do not need to presort

the input data. Presorting, however, can make processing more efficient and less costly.

You can use PROC SQL views in BY-group processing. For complete information, see

SAS SQL Procedure User’s Guide.

Note: SAS/ACCESS Users: If you use SAS views or librefs, see SAS/ACCESS for

Relational Databases: Reference for information about using BY groups in your

SAS programs.

464 Chapter 22 • BY-Group Processing in the DATA Step