[{"_id":{"$oid":"5e49c389e3c23a1da881c1c9"},"name":"New York","good_incidents":{"$numberInt":"50"},"salary":{"$numberInt":"50000"},"bad_incidents":"30"},{"_id":{"$oid":"5e49c3bbe3c23a1da881c1ca"},"name":"Cairo","bad_incidents":{"$numberInt":"59"},"salary":{"$numberInt":"15000"}},{"_id":{"$oid":"5e49c42de3c23a1da881c1cb"},"name":"Berlin","incidents":{"$numberInt":"30"},"bad_incidents":"15","salary":{"$numberInt":"55000"}},{"_id":{"$oid":"5e49c58ee3c23a1da881c1cc"},"name":"New York","good_incidents":{"$numberInt":"15"},"salary":{"$numberInt":"56500"}}]

db.collection.aggregate([{$facet:{repeated_city:[{$group:{_id:"$name",name:{$first:"$name"},count:{$sum:1}}},{$match:{count:{$gt:1}}},{$sort:{count:-1}},{$limit:1}],bad_incidents:[{$group:{_id:null,avg_bad_incidents:{$avg:{$toInt:"$bad_incidents"}}}}],good_incidents:[{$group:{_id:null,max_good_incidents:{$max:{$toInt:"$good_incidents"}}}}],max_salary:[{$match:{bad_incidents:{$exists:false}}},{$group:{_id:null,max_salary:{$max:{$toInt:"$salary"}}}}]}},{$replaceWith:{$mergeObjects:[{$arrayElemAt:["$repeated_city",0]},{$arrayElemAt:["$bad_incidents",0]},{$arrayElemAt:["$good_incidents",0]},{$arrayElemAt:["$max_salary",0]}]}}])