How to perform .Max() on a property of all objects in a collection and return the object with maximum value [duplicate]

Answer 1

The answers so far are great! But I see a need for a solution with the following constraints:

1. Plain, concise LINQ;
2. O(n) complexity;
3. Do not evaluate the property more than once per element.

Here it is:

public static T MaxBy(this IEnumerable en, Func evaluate) where R : IComparable {
    return en.Select(t => new Tuple(t, evaluate(t)))
        .Aggregate((max, next) => next.Item2.CompareTo(max.Item2) > 0 ? next : max).Item1;
}

public static T MinBy(this IEnumerable en, Func evaluate) where R : IComparable {
    return en.Select(t => new Tuple(t, evaluate(t)))
        .Aggregate((max, next) => next.Item2.CompareTo(max.Item2) < 0 ? next : max).Item1;
}

Usage:

IEnumerable> list = new[] {
    new Tuple("other", 2),
    new Tuple("max", 4),
    new Tuple("min", 1),
    new Tuple("other", 3),
};
Tuple min = list.MinBy(x => x.Item2); // "min", 1
Tuple max = list.MaxBy(x => x.Item2); // "max", 4