[{"_id":ObjectId("5e82661d164941779c2380ca"),"name":"something","values":[{"id":1,"val":"x"},{"id":1,"val":"x"},{"id":2,"val":"y"},{"id":1,"val":"xxxxxx"}]}]

db.collection.aggregate([{$addFields:{values:{$reduce:{input:"$values",initialValue:[],in:{$concatArrays:["$$value",{$cond:[{$in:["$$this.id","$$value.id"]},[],["$$this"]]}]}}}}}])