>Assume I have a datatable in a dataset with columns called ItemName and Quantity. Due to changes by the customer, there will now be multiple rows with the same ItemName and a Quantity of 1. The app used to have one row for the item and the total quantity.
>
>How do I combine the DT so that there is again one row with the total quantity?

Do you want to save the totalled datatable to the backend? If so will this just be a one-off (tidy up) operation ?
Or do you just need the totalled version to work with temporarily in the app ?