What does the IN= data set option allow you to do?

The IN= data set option is specifically designed to identify which data sets contain a particular observation within a merged or combined data set. When you use the IN= option, it creates a temporary variable that takes on the value of 1 if the observation originates from the specified data set and 0 if it does not. This functionality is particularly useful in scenarios where you want to keep track of the source of each observation after performing operations such as merging or joining data sets.

In contrast, creating new data sets from multiple sources usually involves procedures like PROC APPEND or DATA step programming without the IN= option. Modifying variable types typically requires the use of functions such as PUT or INPUT within a DATA step, rather than relying on the IN= option. Summarizing data across different data sets often involves using procedures like PROC MEANS, PROC SUMMARY, or PROC REPORT, none of which utilize the IN= data set option for their primary purpose.