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