[FIXED] Fetch max value in a list of objects which are inside list of objects by month using Java Stream

Issue

I have list of Store objects and each Store object has a list of Sales objects. I want to fetch the Store object which has the highest sale for any item for a particular month.

public class Store {
 private String storeName;
 private String contactInfo;
 private List<Sales> sales;

//getter & setter
}
public class Sales {
 private String month;
 private String year;
 private BigInteger price;

//getter & setter
}

As of now I'm able to filter the list of Store objects by month

List<Store> stores = list.stream()
             .filter(s -> s.getPrice().stream().anyMatch(t -> t.getMonth().contains("Jan")))
             .collect(Collections.toList());

But I want to filter this list further to get a single store object which has the max price for the month of January.

EDIT : sample list structure in JSON format

[
   {
      "storeName": "abc",
      "contactInfo": "xcb",
      "sales": [{
                  "month" : "Jan",
                  "year": "2022",
                  "price": 3000
                },
                {
                  "month" : "Feb",
                  "year": "2022",
                  "price": 3300
                }
               ]
   },
   {
      "storeName": "abcde",
      "contactInfo": "xcbe",
      "sales": [{
                  "month" : "Jan",
                  "year": "2022",
                  "price": 2000
                },
                {
                  "month" : "Feb",
                  "year": "2022",
                  "price": 4000
                }
               ]
   }
] 

Thank you!

Solution

You can flat map to pairs of (store, price) and select the max:

stores.stream()
        .flatMap(store -> store.getSales()
                .stream()
                .filter(sales -> sales.getMonth().contains("Jan"))
                .map(sales -> Map.entry(store, sales.getPrice())))
        .max(Entry.comparingByValue())
        .map(Entry::getKey)

Answered By - shmosel
Answer Checked By - Senaida (JavaFixing Volunteer)