17. Practice Exercises with Answer Hints
17.2 GroupBy and Merge
Exercise C. GMV and order count by city for Delivered only. Named aggregations.
Hint C
Filter status first, then groupby("city", as_index=False).agg(gmv=("amount","sum"), orders=("order_id","nunique")).
Exercise D. Left-merge a stores table; list orders with missing city from the store dimension.
Hint D
orders.merge(stores, on="store_id", how="left") then df[df["city"].isna()].