Use groupingBy and filtering out entire groups

Question

I have a list of MyObjects like this

ID	Type	Description
1	Summary
1	Detail	keep this group
1	Detail	keep this group
2	Summary
2	Detail	don't keep this group
2	Detail	don't keep this group

I'd like to group the list by ID and filter out the groups that do not contain any Descriptions with "keep this group" as the value.

Below is what I have tried

   Map<String, List<MyObject>> output =
        myObjectList.stream()
            .collect(Collectors.groupingBy(MyObject::getId,
                    Collectors.filtering(x -> x.getDescription().equals("keep this group"),
                        Collectors.toList())));

This does not really work thought. It creates the groups and removes all elements without "keep this group"

So group 1 has 2 elements and group 2 has 0 elements

I'd like to completely reject group 2 and keep all elements in group 1

Answer 1

I have not tested code. It will remove group which does not have any object description equals "keep this group".

Map<String, List<MyObject>> output =
 myObjectList.stream() 
.collect(Collectors.groupingBy(MyObject::getId))
.entrySet()
.stream()
.filter(e-> e.getValue().stream().filter(o->o.getDescription().equals("keep this group")).count()>0)
.collect(Colletors.toMap(Map.Entry::getKey, Map.Entry::getValue));