How to group elements of a List by elements of another in Java 8

Question

I have the following problem: Given these classes,

class Person {
    private String zip;
    ...
    public String getZip(){
        return zip;
    }
}

class          


        

Answer 1

I have not done any testing of this code, but it compiles so it must be right (:eyeroll:).

public Map> mapPeopleToRegion(List people, List regions){
    final Map> personToRegion = new HashMap<>();
    people.forEach(person ->
          personToRegion.put(
                person,regions.stream().filter(
                      region -> region.getZipCodes().contains(person.getZip()))
                      .collect(Collectors.toList())));
    return personToRegion;
}