change column based on filter

Hi Everyone,

I am trying to write a measure which changes the column used for calculation based on filter selection. 

Example: If the selected filter value is A, measure should calculate using column 1, if selected filter value is B, then the measure should calculate using column 2, if nothing is selected, it should calulate using column 3.

How do I write this measure?

Or I am looking it in a wrong way and need to modify the data model?