Datatables ordering on underlying data

sleepingtiger

I have a date column which i am displaying/rendering as N Days left... So i calculate the difference between the current date, and the date on the row, to display "2 days left" for a deadline. How can i sort on the Date not on the label? By sorting on the label i get 1 Days left, 11 Days left, 9 Days left. I recall there used to be a function that i used to be able to set in older version where i could render the data differently but it would still sort on the data...