Java 8 | Fetch top N unique numbers from list

Below Java 8 example shows how to fetch top N unique numbers from ArrayList.

Traditional looping will require more logic to first remove duplicates, sort numbers and then store N numbers to different list.

Java 8 provides stream API to do all the above steps in single line of code. 

Descending order (N = 3)

	List<Integer> integers = new ArrayList<>();
	integers.add(1);
	integers.add(2);
	integers.add(1);
	integers.add(5);
	integers.add(5);
	integers.add(6);
	integers.add(4);
	integers.add(0);
	integers.stream().sorted((a, b) -> b-a).distinct().limit(3).forEach(System.out::println);
	//Output
	6
	5
	4

view raw DesendingOrder.java hosted with ❤ by GitHub

Ascending order (N = 3)

	List<Integer> integers = new ArrayList<>();
	integers.add(1);
	integers.add(2);
	integers.add(1);
	integers.add(5);
	integers.add(5);
	integers.add(6);
	integers.add(4);
	integers.add(0);
	integers.stream().sorted().distinct().limit(3).forEach(System.out::println);
	//Output
	1
	2
	4

view raw AsendingOrder.java hosted with ❤ by GitHub