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How to intersect multiple sets?

开发者 https://www.devze.com 2023-01-21 13:15 出处:网络
I have this list:开发者_如何学Go private List<Set<Address>> scanList; So my list contains multiple scans as you can see.

I have this list:开发者_如何学Go

private List<Set<Address>> scanList;

So my list contains multiple scans as you can see. After each scan I add new set into the list.

After all scans are finished I would like to take only the addresses that occur in every set and put it into:

private List<Address> addresses;

Does something like this already exists in Set/TreeSet/HashSet?

EDIT: after answers, retainAll() is the right method. Thank you. Here is the source:

Set<Address> addressCross = scanList.get(0);
for (int i = 1; i < scanList.size(); i++) {
    addressCross.retainAll(scanList.get(i));
}   
for (Address address : addressCross) {
    addresses.add(address);
}


you can use retainAll(Collection<?> c), check it out here

A side note: that operation is called intersection.

To convert then it to a List you can use the method addAll(Collection<? extends E> c) which should work between all kinds of containers.

eg:

ArrayList<Address> list = new ArrayList<Address>();
list.addAll(yourSet);


See "retainAll()".


With Guava, you could do it like this:

Set<Address> intersection = scanList.get(0);
for (Set<Address> scan : scanList.subList(1, scanList.size())) {
  intersection = Sets.intersection(intersection, scan);
}
List<Address> addresses = Lists.newArrayList(intersection);

This creates a view of the intersection of all the sets in the scanList and then copies the addresses in the intersection into a List. You would need to ensure your scanList has at least one element in it, of course.


There's another nice solution over here: https://stackoverflow.com/a/38266681/349169

Set<Address> intersection = scanList.stream()
    .skip(1) // optional
    .collect(()->new HashSet<>(scanList.get(0)), Set::retainAll, Set::retainAll);
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