What is the difference between the RETAIN and SUM statement in SAS?

The RETAIN statement is used in SAS to carry forward the value of a variable from one iteration of the DATA step to the next, without resetting it to missing. This is useful for retaining values for calculations or comparisons across observations.

On the other hand, the SUM statement is used in SAS to calculate the sum of values of a variable across observations within a BY group. It is typically used in conjunction with the BY statement to calculate group-specific totals.

In summary, the RETAIN statement retains the value of a variable across iterations of the DATA step, while the SUM statement calculates the sum of values within a group of observations.