[{"result":23232,"temperatures":{"temp_limits":{"min":10,"max":31,},"temp_cities":[{"city":"citie_1","city_temp":[{"temp":17,"date":"2018-12-18T10:35:07.000Z"},{"temp":21,"date":"2018-12-17T11:35:05.000Z"},{"temp":23,"date":"2018-12-17T14:36:07.000Z"},],"locked":false},{"city":"citie_2","city_temp":[{"temp":15,"date":"2018-12-18T14:15:07.000Z"},{"temp":22,"date":"2018-12-17T11:33:02.000Z"}],locked:false}]}}]

db.collection.aggregate([{$addFields:{"temperatures.temp_cities":{$map:{input:"$temperatures.temp_cities",as:"tc",in:{locked:"$$tc.locked",city:"$$tc.city",city_temp:{$let:{vars:{maxDate:{$max:"$$tc.city_temp.date"}},in:{$arrayElemAt:[{$filter:{input:"$$tc.city_temp",cond:{$eq:["$$this.date","$$maxDate"]}}},0]}}}}}}}}])