Hi Dan,
Thanks for your help and for distinguishing the two concepts of "school of thought".
Your simple example file makes sense and it is easy to understand. I found this is just simple but so powerful!
Yes, I will do the sum (x,y) instead of x+y for this.
The "SUM formula" solves the problem and I don't need to do many extra steps to convert missing values to zero, column to column and it is time consuming.
It is a big help! Great to know that JMP covers both concepts of "school of thought"
Have a great day and thanks again.