Min/Max of object.attribute in a list of object with guava

Question

Let's take a list of Person defined as

Name
Surname
Age

I want the max(age) in a List<Person>.

I could iterate on this list and manually keep the max :

Integer max = null;
for(Person p : list) {
  if(max == null || max < p.getAge()) {
    max = p.getAge();
  }
  return max;
}

But I feel that there might exist a combination of Guava methods which can do it for me. If I write a Function<Person, Integer>, is there a ready-to-use method to get the max from the list?

Uh, what is `age`? I take it this is an `Integer` but why not make it an `int`? — fge, Feb 21 '14 at 14:25
I like object because they can be null. If the age is not filled, I prefer getting a NPE (and be forced to add a constraint in DB) instead of having 0. — Arnaud Denoyelle, Feb 21 '14 at 14:28
Uh, OK... But then why not force the code to have a value inserted in a first place? Hint: with null columns, how do you reliably use `NOT IN`? — fge, Feb 21 '14 at 14:30
@fge It is a personal choice. On all the beans of my current project, I only write the attributes and generate Getters/Setters + a default constructor. I personnally hate Setters that do other than just setting a value. For `NOT IN`, I admit that I have never tried to use it on an optional column. — Arnaud Denoyelle, Feb 21 '14 at 14:40

score 4 · Accepted Answer · edited Jan 02 '18 at 20:55

4

See this answer. You can use Ordering.max()

Ordering<People> o = new Ordering<People>() {
    @Override
    public int compare(People left, People right) {
        return Ints.compare(left.getAge(), right.getAge());
    }
};

return o.max(list);

edited Jan 02 '18 at 20:55

Jurn Ho

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answered Feb 21 '14 at 14:17

n1k1ch

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score 1 · Answer 2 · answered Feb 21 '14 at 14:12

You can do it with Guava, but I think it would come out to be more convoluted than a cleaner version of your solution, namely:

int max = -1;

for (People p : list) {
    if (p.getAge() > max)
        max = p.getAge();
}

By the way, it may make more sense to call your class Person, since it is representing a single person, and not a group of people.

score 1 · Answer 3 · answered Feb 21 '14 at 16:53

1

If you have a Function<Person, Integer> (called getAge, say), this would just be:

Integer maxAge = Ordering.natural().max(Iterables.transform(people, getAge));

answered Feb 21 '14 at 16:53

ColinD

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Min/Max of object.attribute in a list of object with guava

3 Answers3