Java 8 Streams : get non repeated counts

Question

Here is the SQL version for the input and output :

     with tab1 as (

        select 1 as id from dual union all
        select 1 as id from dual union all         


        

Answer 1

You may do it like so,

Map countByNumber = myList.stream()
    .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
List uniqueNumbers = myList.stream()
    .filter(n -> countByNumber.get(n) == 1)
    .collect(Collectors.toList());

First create a map using the value and the number of occurences. Then iterate over the List of numbers, get the occurences from the map for each number. If the number of occurences is 1, then collect it into a separate container.

If you want to do it in one go, here it is.

List uniqueNumbers = myList.stream()
    .collect(Collectors.collectingAndThen(Collectors.groupingBy(Function.identity(), 
        Collectors.counting()),
    m -> myList.stream().filter(n -> m.get(n) == 1).collect(Collectors.toList())));