At planned purchase orders user can group by items to sum the quantities of the same item & vendor in one planned purchase order and it helps him to create single line for an individual item in purchase order.
User can process this grouping, item wise one by one by selecting the planned purchase orders of that specific item which is a hectic job and in case of hundred of items its impossible for user to work on it. So there must be a group by option to process the grouping of the selected items or all item (depend upon the user selection) if they have same vendor in their planned purchase orders. right now while selection different items system doesn't not allow to process the group by functionality.