Previous examples of DATA
steps used DO loops to generate one or more observations from one
iteration of the DATA step. It is also possible to write a DATA step
that reads a data set and uses variables in the input data set to
compute the value of a new variable.
The SAS data set Work.CDRates
contains interest rates for certificates of deposit (CDs) that are
available from several institutions.
Suppose you want to
compare how much each CD earns at maturity with an investment of $5,000.
The DATA step below creates a new data set, Work.Compare, that contains
the added variable, Investment.
data work.compare(drop=i);
set work.cdrates;
Investment=5000;
do i=1 to years;
investment+rate*investment;
end;
run;
proc print data=work.compare;
run;
The index variable is
used only to execute the DO loop, so it is dropped from the new data
set. Notice that the data set variable Years is used as the stop value
in the iterative DO statement. As a result, the DO loop executes the
number of times specified by the current value of Years.
Here is what happens
during each iteration of the DATA step:
-
An observation is read from Work.CDRates.
-
The value 5000 is assigned to the
variable Investment.
-
The DO loop executes, based on
the current value of Years.
-
The value of Investment is incremented
(each time that the DO loop executes), using the current value of
Rate.
At the end of the first
iteration of the DATA step, the first observation is written to the
Work.Compare data set. Control returns to the top of the DATA step,
and the next observation is read from Work.CDRates. These steps are
repeated for each observation in Work.CDRates. The resulting data
set contains the computed values of Investment for all observations
that have been read from Work.CDRates.