> db.avgtest.drop()
true
> db.avgtest.insert({nums: [NumberLong("18014398509481984"), NumberLong(1), NumberLong("-18014398509481984"),NumberLong(-1)]})
> db.avgtest.aggregate({$unwind:'$nums'}, {$group: {_id:1, avg:{$avg:'$nums'}}})
{ "result" : [ { "_id" : 1, "avg" : -0.25 } ], "ok" : 1 }