using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        //Create the data source

        List<int> Scores = new List<int>() { 97, 92, 81, 60 };

​

        // Create the query.

        //IEnumerable<int> queryHighScores = Scores.MinByOrDefault(s => s);

        //    from score in Scores

        //    where score > 80

        //    select score;

        List<Test> testers = new List<Test>();

        foreach (var s in Scores)

            testers.Add(new Test(s));

​

        var query = testers.Where(s => s.over).MinByOrDefault(s => s.calculate());

        Console.WriteLine(query != null ? "" + query.calculate() : "null");

​

        var other = testers.Where(s => s.over).Select(s => s.calculate()).MinByOrDefault(s => s);

        Console.WriteLine(other);

        var multiple = testers.Where(s => s.over).Select(s => s.calculate());

        multiple.Min();

        if (!multiple.Any())

            return;

​

        Console.WriteLine("y" + multiple.Min());

        // Execute the query.

        /*foreach (int i in queryHighScores)

        {

            Console.Write(i + " ");

        }   */         

    }

}

​

public class Test

{

    readonly int t = 0;

    public bool over;

​

    public Test(int value)

    {

        t = value;

        over = value > 800;

    }

​

    public int calculate()

    {

        return t;

    }

}

​

public static class exts

{

        static T CompareBy<T, U>(this IEnumerable<T> ts, Func<T, U> selector, int modifier, bool throws)

        {

            var comparer = Comparer<U>.Default;

            T t;

            U u;

            using (var e = ts.GetEnumerator())

            {

                if (!e.MoveNext())

                    if (throws)

                        throw new ArgumentException("Collection must not be empty.", "ts");

                    else

                        return default(T);

                t = e.Current;

                u = selector(t);

                while (e.MoveNext())

                {

                    var nextT = e.Current;

                    var nextU = selector(nextT);

                    if (comparer.Compare(nextU, u) * modifier < 0)

                    {

                        t = nextT;

                        u = nextU;

                    }

                }

​

                return t;

            }

        }

​

    public static T MinByOrDefault<T, U>(this IEnumerable<T> ts, Func<T, U> selector)

    {

        return ts.CompareBy(selector, 1, false);

    }

}