Home Return only the unique values from collection, removing all occurances of duplicates

Questions

Return only the unique values from collection, removing all occurances of duplicates

July 12, 2024

Assuming I have some collection, how could I quickly return only those values that appear exactly once? I don’t want to reduce duplicate values down to a single entry, I want to eliminate them completely – these are non-valid for my use case. As an example, a list containing 1, 2, 3, 1, 4, 3, 5, 1 should only return 2, 4, 5. I could loop over the list, count the elements and then remove all that appear more than once, but I’m wondering if there’s a more elegant .stream()-solution I’m missing.

>Solution :

To return only elements that appear exactly once, you can use Stream to achieve that:

List<Integer> list = Arrays.asList(1, 2, 3, 1, 4, 3, 5, 1);

//Find Number of occurence of each element in the List 

Map<Integer, Long> counts = list.stream()
    .collect(Collectors.groupingBy(e -> e, Collectors.counting()));

// Filter elements that appear only once

List<Integer> result = list.stream()
    .filter(element -> counts.get(element) == 1)
    .toList();