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


i have following problem: given these classes,

class person {     private string zip;     ...     public string getzip(){         return zip;     } }  class region {     private list<string> zipcodes;     ...     public list<string> getzipcodes() {         return zipcodes;     } }

using java 8 stream api, how obtain map<person, list<region>> based on whether region contains person's zip code? in other words how group regions people zip codes belong regions?

i've done in java 7 old fashioned way, have migrate code take advantage of new features in java 8.

thank you,

impeto

i suspect cleanest way -- i'm not quite happy other answers posted -- be

 persons.stream().collect(collectors.tomap(     person -> person,     person -> regions.stream()        .filter(region -> region.getzipcodes().contains(person.getzip()))        .collect(collectors.tolist())));

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