Getting Average in a collection in mongodb -

i new mongodb. want take average, max, min document value in whole collection. able calculate max , min don't know how calculate average or how start it.

this how calculated max.

db.mytable.find({},{"abc":1}).sort({"abc":-1}).limit(1); 

to average whole collection, use aggregation framework $group pipeline operator can specify _id value of null calculate accumulated average value input documents whole:

db.mytable.aggregate([     {         "$group": {              "_id": null,              "avg": { "$avg": "$abc" }          }     } ]);