Sum only columns selected by the user

[bk2799]

Hello all,

I have data set up in the following format:

ID	A	B	C	D	E
1	0	1	1	1	1
2	1	0	1	0	1
3	0	1	1	0	1
4	0	1	1	1	1

I would like to be able to create a user-input filter to use in a measure.  For example, if a user selected columns: "A", "B", and "C" then the measure would calculate SUM(A,B,C)/COLUMN E.

Thanks!