Create Index Values for Every ID, Instead of Every Row

Link to test case: http://live.datatables.net/jidaloxe/9/edit

Description of problem: I am using the RowsGroup plugin to merge News Type and Visibility cells for rows with the same ID. The ID column will be hidden but it is visible in the test case for the sake of better understanding. Now I want to add an index column with index values for every ID, instead of every row. The index column code I am using is from here.

Current result:

Desired result: Note: This image is edited, and is not manipulated through code.

Thanks
Hanz