f7

f7.js

db.albums.ensureIndex( {"images" : 1} );

db.albums.aggregate(
	{ $unwind : "$images" },
	{$group: { _id:null, images: {$addToSet:"$images"}}}
).forEach(function(doc){
	db.images.remove({_id: {$nin: doc.images}});
	// var kittens = db.images.find({tags: "kittens", _id: {$in: doc.images}});
	// print(kittens.count());
});

db.images.find({tags: "kittens"}).count();