To add the result of an expression to an accumulator variable, you can use a sum statement in your DATA step.

The sum statement adds the result of the expression that is on the right side of the plus sign (+) to the numeric variable that is on the left side of the plus sign. The value of the accumulator variable is initialized to 0 instead of missing before the first iteration of the DATA step. Subsequently, the variable’s value is retained from one iteration to the next, as if it had appeared in a RETAIN statement.

To find the total number of elapsed seconds in treadmill stress tests, you need a variable (in this example, SumSec) whose value begins at 0 and increases by the amount of the total seconds in each observation. To calculate the total number of elapsed seconds in treadmill stress tests, you use the sum statement shown below:

data clinic.stress; 
   infile tests; 
   input ID $ 1-4 Name $ 6-25 RestHR 27-29 MaxHR 31-33 
            RecHR 35-37 TimeMin 39-40 TimeSec 42-43 
            Tolerance $ 45; 
   TotalTime=(timemin*60)+timesec; 
   SumSec+totaltime; 
run;

The value of the variable on the left side of the plus sign (here, SumSec) begins at 0 and increases by the value of TotalTime with each observation.

In the previous example, the sum variable SumSec was initialized to 0 by default before the first observation was read. But what if you want to initialize SumSec to a different number, such as the total seconds from previous treadmill stress tests?

You can use the RETAIN statement to assign an initial value other than the default value of 0 to a variable whose value is assigned by a sum statement.

The RETAIN statement serves several purposes:

Suppose you want to add 5400 seconds (the accumulated total seconds from a previous treadmill stress test) to the variable SumSec in the Clinic.Stress data set when you create the data set. To initialize SumSec with the value 5400, you use the RETAIN statement shown below.

data clinic.stress; 
   infile tests; 
   input ID $ 1-4 Name $ 6-25 RestHR 27-29 MaxHR 31-33 
         RecHR 35-37 TimeMin 39-40 TimeSec 42-43 
         Tolerance $ 45; 
   TotalTime=(timemin*60)+timesec; 
   retain SumSec 5400;     
   sumsec+totaltime; 
run;

Now the value of SumSec begins at 5400 and increases by the value of TotalTime with each observation.