Can I stream the difference between two lists where a field is set to something specific in Java?-CodePudding

I have the following class:

public class Person {
    private String name;
    private String gender;
}

Then I have two lists of persons

List A:

index 0: name: "Mike", gender: "male"
index 1: name: "Jane", gender: "female"
index 2: name: "Ellen", gender: "female"
index 3: name: "Ben", gender: "male"
index 4: name: "Jimmy", gender: "male"
index 5: name: "Maria", gender: "female"

List B:

index 0: name: "Ben", gender: "male"
index 1: name: "Maria", gender: "female"
index 2: name: "Jane", gender: "female"
index 3: name: "Brian", gender: "male"
index 4: name: "Sofia", gender: "female"
index 5: name: "John", gender: "male"
index 6: name: "Jimmy", gender: "male"

I want to create a new list of names of all the males that is NOT in both lists.

So from the example the list would look like this:

index 0: name: "Mike", gender: "male"
index 1: name: "John", gender: "male"
index 2: name: "Brian", gender: "male"

The tricky things here is that the filtering goes both ways. I want the final list to contain both males that are in list A but not in list B, and males that are in list B but not in list A. I've not been able to find out how to do this, but I've tried to accomplish it using streams..

CodePudding user response：

not super efecient but works

List<Person> r =
  Stream.concat(
    a.stream().filter(e -> e.isMale() && !b.contains(e)),
    b.stream().filter(e -> e.isMale() && !a.contains(e))
  )
  .collect(Collectors.toList());

more readable versions with storing parial results

List<Person> aNotB = a.stream().filter(e -> e.isMale() && !b.contains(e)).collect(Collectors.toList());
List<Person> bNotA = b.stream().filter(e -> e.isMale() && !a.contains(e)).collect(Collectors.toList());
List<Person> r = new ArrayList<>(aNotB);
r.addAll(bNotA);

CodePudding user response：

List<String> malesNotInBothLists = listA.stream()
    .filter(p -> p.getGender().equals("male"))
    .filter(p -> !listB.stream().anyMatch(b -> b.getName().equals(p.getName())))
    .map(Person::getName)
    .collect(Collectors.toList());

malesNotInBothLists.addAll(listB.stream()
    .filter(p -> p.getGender().equals("male"))
    .filter(p -> !listA.stream().anyMatch(a -> a.getName().equals(p.getName())))
    .map(Person::getName)
    .collect(Collectors.toList()));`enter code here`