How to Get Linq to Return the Object Which Has the Max Value for a Given Property

How to use LINQ to select object with minimum or maximum property value

People.Aggregate((curMin, x) => (curMin == null || (x.DateOfBirth ?? DateTime.MaxValue) <
    curMin.DateOfBirth ? x : curMin))

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

We have an extension method to do exactly this in MoreLINQ. You can look at the implementation there, but basically it's a case of iterating through the data, remembering the maximum element we've seen so far and the maximum value it produced under the projection.

In your case you'd do something like:

var item = items.MaxBy(x => x.Height);

This is better (IMO) than any of the solutions presented here other than Mehrdad's second solution (which is basically the same as MaxBy):

• It's O(n) unlike the previous accepted answer which finds the maximum value on every iteration (making it O(n^2))
• The ordering solution is O(n log n)
• Taking the Max value and then finding the first element with that value is O(n), but iterates over the sequence twice. Where possible, you should use LINQ in a single-pass fashion.
• It's a lot simpler to read and understand than the aggregate version, and only evaluates the projection once per element

How can I use LINQ to get the instance with the highest value of a property in a child list?

You can select the count of each item in SecondClass and use Max to find the maximum value. Then you select this value of each item in FirstClass and use Max again:

int highestCount = input.Select(x => x.SecondClass.Select(y => y.Count).Max()).Max();

If you want to find the item with the highest count, you can replace the first Select by OrderByDescending and the second Max by FirstOrDefault:

var itemWithHighestCount = input.OrderByDescending(x => x.SecondClass.Select(y => y.Count).Max()).FirstOrDefault();

Online demo: https://dotnetfiddle.net/0rWARC

Better way to return an object by max() in LINQ

One liner

  var item = Users.OrderByDescending(x => x.MonthlyWage).FirstOrDefault();

  if(item != null)
    Console.WriteLine("{0}: {1} {2} MAX", item.ID, item.Name, item.MonthlyWage);

  Console.ReadLine();

If we want all top earners:

var wageGroups = from u in Users
                group u by u.MonthlyWage into ug
                orderby ug.Key descending
                select new { MonthlyWage = ug.Key, Users = ug.ToList() };

var topEarners = wageGroups.First().Users;

foreach (var item in topEarners)
{
    Console.WriteLine("{0}: {1} {2} MAX", item.ID, item.Name, item.MonthlyWage);
}

Console.ReadLine();

How can I get LINQ to return the index of the object which has the max value in a collection?

Well, if you wanted to, you could of course write an IndexOfMaxByextension yourself.

Example(untested):

public static int IndexOfMaxBy<TSource, TProjected>
    (this IEnumerable<TSource> source,
     Func<TSource, TProjected> selector,
     IComparer<TProjected> comparer = null
    )
{

    //null-checks here

    using (var erator = source.GetEnumerator())
    {
        if (!erator.MoveNext())
            throw new InvalidOperationException("Sequence is empty.");

        if (comparer == null)
            comparer = Comparer<TProjected>.Default;

        int index = 0, maxIndex = 0;
        var maxProjection = selector(erator.Current);

        while (erator.MoveNext())
        {
            index++;
            var projectedItem = selector(erator.Current);

            if (comparer.Compare(projectedItem, maxProjection) > 0)
            {
                maxIndex = index;
                maxProjection = projectedItem;
            }
        }
        return maxIndex;
    }
}

Usage:

var indexOfPointWithHighestItem2 = myList.IndexOfMaxBy(x => x.Item2);

C# Using LINQ to filter each Object with Max Value in List of Objects

You can achieve the desired result at once with a simple GroupBy and subsequent ordering within each group:

var highestByTitle = list
    .GroupBy(t => t.title)
    .Select(g => g.OrderByDescending(t => t.val).First())
    .ToList();

Demo.

How to get the max value of a function in a list of objects (C#) ? -Beginner-

You need to use maximumArea to store the max of the list, not the max of the current pair.

Trapezoid maximumArea = new Square(0);  //Smallest possible trapezoid

foreach (Trapezoid t in Shape)
{
    if (t.Area() > maximumArea.Area()) maximumArea = t;
}
Console.WriteLine(maximumArea);

You can also shorten this considerably using LINQ:

var maximumArea = shape.OrderByDescending( x => x.Area() ).First();

And if there's a chance that some trapezoids will tie, maybe you should get a list:

var max = shape.Max( x => x.Area() );
var maximumAreas = shape.Where( x => x.Area() == max).ToList();

LINQ: Getting the row with the maximum value of a given attribute

One alternative would be to use:

rows.Select(x => x.OrderByDescending(y => y.StatusDate).First());

... and check that the query optimiser knows that it doesn't really need to sort everything. (This would be disastrous in LINQ to Objects, but you could use MaxBy from MoreLINQ in that case :)

(Apologies for previous version - I hadn't fully comprehended the grouping bit.)

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