In this lesson, we spent time investigating various issues that concern reading one SAS data set into another SAS data set. We explored the many ways in which a SAS data set can be modified, such as using an accumulator variable to sum the contents of another variable and using a SELECT group to assign values conditionally. We also learned how to use a SET and BY statement together in order to be able to identify the first and last observations in a group. We also learned how to detect the end of a data set. Finally, we closed out the lesson by discussing the steps SAS takes when reading in a SAS data set. The homework for this lesson will give you more practice with these techniques so that you become even more familiar with how they work and can use them in your own SAS programming.