Choose the first N classes for proc glm

[liyongkai800]

Say, I have a program like this, where x1 is a categorical variable with 5 levels, and x2, x3 are continuous variables.

proc glm data=mydata;

class x1;

model y=x1 x2 x3;

run;

However, I'm pretty sure that only the first 3 levels of x1 are significant to y. Is there any way to only include the first 3 levels of x1 in the model statement? Thanks.

[Reeza · Accepted solution]

You can add a WHERE statement to your PROC. In general this works across most procedures.

[liyongkai800]

Thanks, I complicate the question too much.