Imagine you have a "shopping cart" full of items. Each item has a unique "SellerID".

Now I would like to create an order in the database PER sellerID.

That means I would have to split the shopping cart, basically an array full of items, into individual arrays, split by the respective sellerID.

Sure I can iterate over the sellerIDs and could, "if sellerID == item.sellerID populate some other array, but that's where I'm stuck right now.