Before you process one or more SAS data sets using
grouped or ordered data with the SET, MERGE, or UPDATE statements,
you must check the data to determine whether they require 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.