What is the purpose of the RETAIN statement?

The RETAIN statement serves a specific and crucial function in SAS programming by preserving the value of a variable across iterations of the DATA step. Normally, in a DATA step, variable values are set and then reset to missing at the beginning of each iteration. By using the RETAIN statement, you can instruct SAS to maintain the value of the specified variable from one iteration to the next. This is especially useful for cumulative calculations, running totals, or any scenario where you want to carry forward a value through the successive observations.

For example, if you're calculating a running total and need to keep the previous total as you iterate through the dataset, the RETAIN statement allows you to do this without losing the accumulated value at the end of each loop. Thus, it plays a vital role in data manipulation and management within a single DATA step, facilitating ongoing calculations and data transformations without the need for additional variables or complex programming logic.