There
are times when you want to modify the observations in a SAS data set
without replacing the data set. You can do this in a DATA step with
the MODIFY statement. Using the MODIFY statement, you can replace,
delete, or append observations in an existing data set without creating
an additional copy of the data. In this chapter, you learn to modify
all the observations in a data set, match observations using a BY
statement, and locate observations using an index.
When
you modify data, it is often essential to safeguard your data and
track the changes that are made. In this chapter you learn how to
create integrity constraints to protect your data. You also learn
two different methods of tracking changes, audit trails and generation
data sets. You use audit trails to track changes that are made to
a data set in place, and you use generation data sets to track changes
that are made when the data set is rebuilt.