hi I really didn't get you in full what you are trying to do.
in my example F1,F2 are Field names I just took for example, you can give any meaningful names to them.
You will not be able to refer column(0), column(1).. etc as you are disabling expressions based on your need.
When you disable any column it wont know that there is one column and it ignores the disabled column and counts sequentially. But in your expression it always refers to 3 columns but in reality there will be only 2 enabled. So this wont work out for your requirement