How to Find Max Date in List<Object>

How to find Max Date in List<Object>?

Since you are asking for lambdas, you can use the following syntax with Java 8:

Date maxDate = list.stream().map(u -> u.date).max(Date::compareTo).get();

or, if you have a getter for the date:

Date maxDate = list.stream().map(User::getDate).max(Date::compareTo).get();

How to get object from list with maximum date time object

I'm assuming that begin is a java.util.Date or any other Comparable? Then you could do:

public ContactData getLatestContact(ContactData[] contacts) {
    return Stream.of(contacts).sorted((a, b) -> DateTimeToolkit.compare(a.begin, b.begin)).findFirst().get();
}

Find object with max date in a list where date property is a String

Assuming that MyObject::getDate returns a format that is acceptable for LocalDate.parse, you are nearly correct. You just need to write a lambda expression:

Comparator.comparing(o -> LocalDate.parse(o.getDate()))

comparing takes a Function<MyObject, T>. You are supposed to give it a method that takes a MyObject and returns something (that extends Comparable) for it to compare.

Learn more about lambdas here.

Getting object with max date property from list of objects Java 8

and the Contact class should not always use the lastUpdated variable
for comparing instances

So you will have to provide a custom comparator whenever you want to compare multiple instances by their lastUpdated property, as it implies that this class is not comparable by default with this field.

Comparator<Contact> cmp = Comparator.comparing(Contact::getLastUpdated);

As you know you can either use Collections.max or the Stream API to get the max instance according to this field, but you can't avoid writing a custom comparator.

Get the highest date in a List of object and get another property of its class

Just order by the date and take the Id property from the first item:

var maxDateId = dtp
    .OrderByDescending(x => x.TDateTime)
    .FirstOrDefault()?.Id;

FirstOrDefault can return null if the sequence is empty, which is why I use the null conditional operator (?.) to access the Id property. If the sequence is empty, maxDateId will be null, so you might have to check for this to make your code safe from a NullReferenceException.

how to find biggest and smallest date in a list?

Why not use Collections.sort() and then take the first/last entries? You can either use natural ordering, or specify your own Comparator.

Note this will sort the collection in-place. It won't give you a new sorted collection.

Sort max date from Object

Your filter callback function is not performing a comparison to filter the correct element. Also, although applying the "maximum" algorithm on the dates as string would be fine in your case (because of the date format you have), it would be much safer to transform the date strings into date objects to consistantly get correct results regardless of the format.

In the solution below, you can use a combination of Array.map() and Array.sort() to copy and process your data in the correct result.

const data = [{
    'scores': [{
        'score': 10,
        'date': '2021-06-05T00:00:00'
    }],
    'id': '3212'
}, {
    'scores': [{
        'score': 10,
        'date': '2021-06-05T00:00:00'
    }, {
        'score': 20,
        'date': '2021-05-05T00:00:00'
    }],
    'id': '123'
}, {
    'scores': [{
        'score': 5,
        'date': '2021-05-05T00:00:00'
    }],
    'id': '321'
}];

// map the data and return the updated objects as the result
const result = data.map((user) => {
    // copy the scores array to not mutate the original data
    const sortedScores = user.scores.slice();
    // sort the scores array by date descending
    sortedScores.sort((a, b) => (new Date(b.date) - new Date(a.date)));
    // return the same user with the first score from the sorted array
    return {
        ...user,
        scores: [sortedScores[0]]
    };
});

console.log(result);

let highestDate = latestReceiptInfoArray
    .compactMap { $0.expiresDate }
    .max()

let highestReceiptInfo = latestReceiptInfoArray
    .filter { $0.expiresDate != nil }
    .max { $0.expiresDate! < $1.expiresDate! }