[{id:1,name:"Bob",age:23},{id:1,name:"Susan",age:32},{id:2,name:"Jeff",age:45}]

db.collection.aggregate([{$facet:{firstQuery:[{$match:{"id":1}},{$group:{_id:null,avg_age:{$avg:"$age"}}}],secondQuery:[{$match:{"id":1}},{$group:{_id:"$name"}}]}}])