hi:
in popgroup dop's Rule parameter i write:
random(@id)<0.1;
@P.x<0;
@Cd.b<0.1;
no one works for me

and if i choose Random Parameter, how do the Use Vexpression works? i tried some expression in it,no one changed the default result.

and how can i see the group information, like in sop's operator information?

You should use the ingroup vex function like this:

ingroup = 1; //add to group
ingroup = 0; //remove from group

example: ingroup = @P.y>1;

Hope that helps!!

oh thank you very much.how can't i call to mind of that ops: