Sort a List based on the values in a map-CodePudding

I am trying to sort a List of objects based on the values in the Map.

LinkedHashMap<String, Integer> map = new HashMap<>();
map.put("1233", 30);
map.put("1562", 5);
map.put("1243", 10);
map.put("1872", 20);

Based on values in this map I want to sort the following list:

l = [ 
     { id:1562,name:"xxx" },
     { id:1233,name:"yyy" },
     { id:1243,name:"zzz" },
     { id:1872,name:"xxx" }

    ]

Expected output:

l = [ 
     { id:1233,name:"yyy" },
     { id:1872,name:"xxx" },
     { id:1243,name:"zzz" },
     { id:1562,name:"xxx" }
    ]

I have tried bubble sort with specific condition but it is taking too much time:

 int n = l.size();
 for (int i = 0; i < n - 1; i  ) {
    for (int j = 0; j < n - i - 1; j  ) {
        if (map.get(l.get(j) > map.get(l.get(j 1)) {
            swap(j, l);
        }
    }
}

 private void swap(int j, List<L> l) {
        l temp = l.get(j);
        l.set(j, l.get(j   1));
        l.set(j   1, temp);
    }

Is there any better option, or any other data structure?

CodePudding user response：

You could do it in one line using the method sort and a comparator, but not sure if it is effcient enough for your use case.

import java.util.Comparator;

.....

l.sort(Comparator.comparing(f -> map.get(f.getId()),Comparator.reverseOrder()));

CodePudding user response：

As I understand the problem, you want to sort a list of entries List<Map.Entry<Integer, String>> based on the values returned by my map Map<String, Integer> for each key in the descending order.

For that, you need to define a Comparator that will compare list elements based on entry keys:

Comparator<Map.Entry<Integer, String>> byKeyDesc =
            Comparator.<Map.Entry<Integer, String>>comparingInt(entry -> 
                    map.get(String.valueOf(entry.getKey()))).reversed();

And then and apply list.sort().

public static void main(String[] args) {
    Map<String, Integer> map =
            Map.of( "1233", 30, "1562", 5,
                    "1243", 10, "1872", 20);

    List<Map.Entry<Integer, String>> entryList = new ArrayList<>(
            List.of(Map.entry(1562, "xxx"),
                    Map.entry(1233, "yyy"),
                    Map.entry(1243, "zzz"),
                    Map.entry(1872, "xxx"))
    );

    Comparator<Map.Entry<Integer, String>> byKeyDesc =
            Comparator.<Map.Entry<Integer, String>>comparingInt(entry ->
                    map.get(String.valueOf(entry.getKey()))).reversed();

    entryList.sort(byKeyDesc);
    entryList.forEach(System.out::println);
}

Output

1233=yyy
1872=xxx
1243=zzz
1562=xxx