Why do you want to use index instead of 3 fields? One can provide other ways to accomplish the requirement.
One way I can think of is - concatenate the 3 values in one variable and export it. Now, import the same variable in called program and use the 3 values by splitting the variable. But again, if this is not critical requirement, I would go with 3 export/imports.
Unless you try to do something beyond what you have already mastered, you will never grow!