[basex-talk] how to count and remove "entities"

Not sure of the correct lingo, but I'm building a database of tweets. As I run it, duplicate tweets are added to the database. I can see the duplicates with:

for $tweets in db:open("twitter") return <tweet>{$tweets/json/id__str}</tweet>

Firstly, how would I select the json node for a duplicate entity. But, before even selecting that node, recursively look to see if there's more than one result for that id__str value.

How would I even generate a count of each occurrence for the data of a specific id__str?

thanks,

Thufir