Is this a native grid you’re adding a custom column to? If so, I would probably go this route first: Showing UD Field values from JobHead in Job Entry LandingPage View - Kinetic ERP - Epicor User Help Forum
If that didn’t work, I would send the dataset to the function, process there, then send it back.
I would save the dataview-condition for a last resort as it’s not the most efficient.