- is a method of processing observations from
one or more SAS data sets that are grouped or ordered by values of one or
more common variables. The most common use of BY-group processing in the DATA
step is to combine two or more SAS data sets by using the BY statement with
a SET, MERGE, MODIFY, or UPDATE statement.
- BY variable
- names a variable or variables by which the
data set is sorted or indexed. All data sets must be ordered or indexed on
the values of the BY variable if you use the SET, MERGE, or UPDATE statements.
If you use MODIFY, data does not need to be ordered. However, your program
might run more efficiently with ordered data. All data sets that are being
combined must include one or more BY variables. The position of the BY variable
in the observations does not matter.
- BY value
- is the value or formatted value of the BY
- BY group
- includes all observations with the same
BY value. If you use more than one variable in a BY statement, a BY group
is a group of observations with the same combination of values for these variables.
Each BY group has a unique combination of values for the variables.
- are variables that SAS creates for each
BY variable. SAS sets FIRST.variable when it
is processing the first observation in a BY group, and sets LAST.variable when it is processing the last observation in a BY
group. This allows you to take different actions, based on whether processing
is starting for a new BY group or ending for a BY group. For more information,
How the DATA Step Identifies BY Groups.
For more information about BY-Group processing, see
Reading, Combining, and Modifying SAS Data Sets.
Combining and Modifying SAS Data Sets: Examples.
Copyright 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.