Column and Row Indexes
The following indexes can be used in methods and callback functions:
Initial Column Index (or simply Column Index)
Equals the column's index in the columns array.
Do not confuse the visible column index with the index specified using the column.visibleIndex option. The latter is used in column reordering.
Starts from 0 and increases by 1 per row including group rows. With paging, the index resets on each page.