How to perform arithmetic on the result of Collectors.Counting()?

Given:

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

Return:

an Integer = Sum(((Frequency of Integer) / 2)))

I’m able to get the frequency of each integer using Collectors.groupingBy(), but want to then divide each frequency value by 2 and then sum all the values in the map, returning just an Integer:

Map<Integer, Long> myIntegerMap = myIntegers.stream().collect(Collectors.groupingby(Function.identity(), Collectors.counting()));

for(Map.Entry<Integer, Long> a : myIntegerMap.entrySet()){ System.out.print(a.getKey(), + "==>"); System.out.println(a.getValue());}

Output:

1 ==> 2

2 ==> 2

3 ==> 1

4 ==> 1

Desired Output:

( ( 2 / 2 ) + ( 2 / 2 ) + ( 1 / 2 ) + ( 1 / 2 ) ) = 2

>Solution :

You can do that with a map-reduce approach like so:

  long result = myIntegerMap.values().stream()
            .mapToLong(aLong -> aLong / 2)
            .sum();

Hope I didn’t misunderstand your question and this helps.