Sorting a number of lists based on two lists in Java

Question

I have four lists as follows:

    ArrayList<String> tempNameList = new ArrayList<>();
    ArrayList<String> tempPhoneList = new ArrayList<>();
    ArrayList<String> tempAddressList = new ArrayList<>();
    ArrayList<String> tempBirthdayList = new ArrayList<>();

Each list contains records related to the other lists by index. I am trying to sort all the lists in ascending order by the person's Name and Birthday. I have tried using Collections.sort() but it only supports a single list at a time.
How do I sort all the lists by name and birthday?

I mean `List` where `class Person` contains fields `name`, `phone`, `address` and `birthday`. — shmosel, Dec 24 '21 at 04:50
@shmosel I haven't tried that yet. My code is completed using Lists. How do I sort it using classes? I can change my code — JAMSHAID, Dec 24 '21 at 04:53
This code shows classic “object phobia”. Create a person (or whatever name makes sense) object. Parallel arrays are not great OO. — Boris the Spider, Dec 24 '21 at 04:55
@hfontanez could you please share a link ? Or else I will write a new code. Thanks — JAMSHAID, Dec 24 '21 at 05:09
It's the same that shmosel recommended. But, in order to sort a `Person` the class needs to implement `Comparable`. — hfontanez, Dec 24 '21 at 05:12
found similar question, https://stackoverflow.com/q/30821395 have a look you'll get help here — Zakir Hussain, Dec 24 '21 at 05:18
You should also convert the birthdays to actual date because in general case their sorting largely depends on the format, that is, the birthdays can be sorted only if they are presented in YYYY-MM-DD or similar format (with leading zeroes in month/day) — Nowhere Man, Dec 24 '21 at 06:56

score 1 · Answer 1 · answered Dec 24 '21 at 08:11

Sorting of multiple lists of the same size is possible following these steps:

Create an array/list of indexes according to the sorting rules (first by names, then by birthdays in appropriate YYYYMMDD format, etc.)

List<String> names  = Arrays.asList("bbb", "aaa", "bbb", "aaa");
List<String> phones = Arrays.asList("1023456", "1324560", "1227890", "1446752");
List<String> bdays  = Arrays.asList("20001122", "19980105", "20010614", "19990507");

int[] indexes = IntStream.range(0, names.size())
    .boxed()
    .sorted(Comparator.comparing(names::get).thenComparing(bdays::get))
    .mapToInt(Integer::intValue)
    .toArray(); // -> [1, 3, 0, 2]

Reorder each of the input lists according to the indexes. A separate method may be created for this:

private static List<String> sort(List<String> list, int[] indexes) {
    return Arrays.stream(indexes).mapToObj(list::get).collect(Collectors.toList());
}
// ...
System.out.println(sort(names,  indexes)); -> [aaa, aaa, bbb, bbb]
System.out.println(sort(phones, indexes)); -> [1324560, 1446752, 1023456, 1227890]
System.out.println(sort(bdays,  indexes)); -> [19980105, 19990507, 20001122, 20010614]

However, it would be more natural to create a container object to combine the values from the different input lists, which has become quite simple after introducing record classes in Java 16, and the sort these objects:

record Person(String name, String phone, String bday) {}

List<Person> persons = IntStream.range(0, names.size())
    .boxed()
    .map(i -> new Person(names.get(i), phones.get(i), bdays.get(i)))
    .sorted(Comparator.comparing(Person::name).thenComparing(Person::bday))
    .collect(Collectors.toList());

persons.forEach(System.out::println);

Output:

Person[name=aaa, phone=1324560, bday=19980105]
Person[name=aaa, phone=1446752, bday=19990507]
Person[name=bbb, phone=1023456, bday=20001122]
Person[name=bbb, phone=1227890, bday=20010614]

Sorting a number of lists based on two lists in Java

1 Answers1