Stream expressions: Break up multivalue field into usable tuples

[Doug Turnbull]

I have a field like follows in my search index

{
   "shopper_id": 1234,
   "basket_id": 2512,
   "items_bought": ["eggs", "tacos", "nachos"]
}

{
   "shopper_id" 1236,
   "basket_id": 2515,
   "items_bought": ["eggs", "tacos", "chicken", "bubble gum"]
}

I would like to use some of the stream expression capabilities (in this
case I'm looking at the recsys stuff) but it seems like I need to break up
my data into tuples like

{
   "shopper_id": 1234,
   "basket_id": 2512,
    "item": "egg"
},
{
   "shopper_id": 1234
   "basket_id": 2512,
   "item": "taco"
}
{
   "shopper_id": 1234
   "basket_id": 2512,
   "item": "nacho"
}
...

For various other reasons, I'd prefer to keep my original data model with
Solr doc == one shopper basket.

Now is there a way to take documents above, output from a search tuple
source and apply a stream mutator to emit baskets with a field broken up
like above? (do let me know if I'm missing something completely here)

Thanks!
-Doug