When using 'groupBy' how to have access to another property?

[williamxsp]

Im grouping by a property but id like to have access to another property.
In this example, im grouping by city but cant use the 'city name' because cities can have the same name, so im using the city_id.
How can I have access to the 'city_name' property?

Stackblitz which reproduces described behaviour