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

For completeness, here's a Java 8 way which doesn't make use of streams:

Map frequencyMap = new LinkedHashMap<>(); // preserves order

myList.forEach(element -> frequencyMap.merge(element, 1L, Long::sum)); // group, counting

frequencyMap.values().removeIf(count -> count > 1); // remove repeated elements

Set nonRepeated = frequencyMap.keySet(); // this is your result

This uses Map.merge to fill the map with the count of each element. Then, Collection.removeIf is used on the values of the map, in order to remove the entries whose value is greater than 1.

I find this way much more compact and readable than using streams.