What happens when you use this highlighted statement in your program: if _N_=1 then do; if 0 then set pg3.stocks(keep=Stock Date Open Close); end;

The highlighted statement utilizes the conditional execution features of SAS programming, specifically with the _N_ automatic variable and the SET statement. Here’s a breakdown of the components and the overall effect of this statement.

When the code checks if _N_=1, it implies that the block of code that follows will only execute during the first iteration of the DATA step. However, when the next condition if 0 is applied, which is logically false, it restricts the execution of the enclosed block (including the SET statement). Since this block does not execute due to the if 0, the SET statement isn't processed at all.

1. Using if _N_=1: At the start of the DATA step, _N_ equals 1 for the first observation, so this part of the code is evaluated. However, the inner condition if 0 is never true, preventing any action from occurring.

2. Effect on Data Set ( SET ** statement)**: Because the condition that follows is false, SAS completely skips executing the SET statement. Thus, no data is read into the Program Data Vector (PDV) from the `