How would you keep a variable during a DATA step operation that you want to initialize or retain across iterations?

The RETAIN statement is used in SAS to ensure that the value of a variable is maintained across iterations of the DATA step. When a variable is retained, it does not get reset to missing at the start of each iteration; instead, it retains its value from the previous iteration, allowing for cumulative calculations or ongoing record tracking.

This mechanism is particularly useful in scenarios where a variable needs to accumulate values or maintain state information throughout the DATA step processing. For example, if you're calculating a running total where each iteration adds to the previous total, RETAIN is the appropriate tool to achieve this.

The KEPT statement does not fulfill the same role, as it determines which variables are included in the output data set but does not affect how they are treated during the DATA step's iterations. Additionally, defining a variable as temporary does not serve the purpose of retaining its value; temporary variables are not saved when the DATA step completes. Declaring a variable at the end of the DATA step also does not apply here because it happens after all iterations have processed rather than maintaining it during the processing. Thus, using the RETAIN statement is essential for maintaining a variable's value across iterations in a DATA step.