What happens to new variables in the PDV before the next observation is read?

In the Program Data Vector (PDV) of SAS, new variables are initialized to missing before the next observation is read. This process is important because it ensures that each time a new observation is processed, any previously unassigned variables do not carry over values from previous observations, which could lead to incorrect analysis.

When a new observation is read into the PDV, SAS creates a new logical space for the data and initializes any new variables. This feature helps maintain data integrity and ensures that results derived from the data reflect only the current observation. Consequently, if those variables have not been assigned a value in the current iteration, they will be missing, allowing for clear identification of missing data during analysis.

This behavior is essential for proper data management and analysis within the SAS environment, making it easier for programmers to handle variable initialization within their data steps.