How can I get LINQ to return the object which has the max value for a given property? [duplicate]

Question

If I have a class that looks like:

public class Item
{
    public int ClientID { get; set; }
    public int ID { get; set; }
}

And a collection of those items...

List<Item> items = getItems();

How can I use LINQ to return the single "Item" object which has the highest ID?

If I do something like:

items.Select(i => i.ID).Max(); 

I'll only get the highest ID, when what I actually want returned is the Item object itself which has the highest ID? I want it to return a single "Item" object, not an int.

Answer 1

This will loop through only once.

Item biggest = items.Aggregate((i1,i2) => i1.ID > i2.ID ? i1 : i2);

Thanks Nick - Here's the proof

class Program
{
    static void Main(string[] args)
    {
        IEnumerable<Item> items1 = new List<Item>()
        {
            new Item(){ ClientID = 1, ID = 1},
            new Item(){ ClientID = 2, ID = 2},
            new Item(){ ClientID = 3, ID = 3},
            new Item(){ ClientID = 4, ID = 4},
        };
        Item biggest1 = items1.Aggregate((i1, i2) => i1.ID > i2.ID ? i1 : i2);

        Console.WriteLine(biggest1.ID);
        Console.ReadKey();
    }


}

public class Item
{
    public int ClientID { get; set; }
    public int ID { get; set; }
}  

Rearrange the list and get the same result

Answer 2

.OrderByDescending(i=>i.id).First()

Regarding the performance concern, it is very likely that this method is theoretically slower than a linear approach. However, in reality, most of the time we are not dealing with the data set that is big enough to make any difference.

If performance is a main concern, Seattle Leonard's answer should give you linear time complexity. Alternatively, you may also consider to start with a different data structure that returns the max value item at constant time.

First() will do the same as Take(1) but returns the item directly instead of an enumeration containing the item.

Answer 3

int max = items.Max(i => i.ID);
var item = items.First(x => x.ID == max);

This assumes there are elements in the items collection of course.