[{"_id":"1","email":"c@c.com","materials":[{"_id":"1","title":"MDF 18mm Blanco","id":"mdf18blanco","thickness":"18","family":"MDF","color":""},{"_id":2,"family":"Melamina",},{"_id":3,"family":"MDF",}]}]

db.collection.aggregate([{"$match":{"email":"c@c.com"}},{"$unwind":"$materials"},{"$group":{"_id":"$_id","list":{"$addToSet":"$materials.family"}}}])