using System;

using System.Collections.Generic;

using System.Linq;

​

using BenchmarkDotNet.Attributes;

using BenchmarkDotNet.Running;

​

//https://stackoverflow.com/questions/77340562/orderby-with-custom-comparer-performs-much-slower-than-default-comparer

​

public class Program

{

    public class ColumnComparer : IComparer<Row>

    {

        public ColumnComparer(int column)

        {

            Column = column;

        }

​

        public int Column { get; }

​

        public int Compare(Row x, Row y) => x.Values[Column].CompareTo(y.Values[Column]);

    }

​

    public class DummyComparer<T> : IComparer<T>

    {

        public int Compare(T x, T y) => throw new ApplicationException($"Here is the traceback at which IComparer<{typeof(T).Name}>.CompareTo(x, y) is called");

    }

    public class Row

    {

        public int Index { get; }

​

        public List<double> Values { get; } = new();

​

        public Row(int index)

        {

            Index = index;

        }

    }

​

    public class Sort

    {

        private readonly List<Row> _rows;

​

        public Sort()

        {

            _rows = new List<Row>();

            var r = new Random(0);

​

            // Ran out of memoru using 500000

            for (int i = 0; i < 45000; ++i)

            {

                var row = new Row(i);

                for (int j = 0; j < 32; ++j)

                {

                    row.Values.Add(r.Next(0, 1000));

                }

​

                _rows.Add(row);

            }

        }

​

        [Benchmark]

        public void Sort1()

        {

            var sort2 = _rows.OrderBy(x => x.Values[8]).ToArray();

        }

​

        [Benchmark]

        public void Sort2()

        {

            var comparer = new ColumnComparer(8);

            var sort2 = _rows.OrderBy(e => e, comparer).ToArray();

        }

        [Benchmark]

        public void Sort3()

        {

            var sort3 = _rows

                .Select(row => (row, value : row.Values[8])) // Precompute the value

                .OrderBy(p => p.value)                       // Compare the value

                .Select(p => p.row).ToArray();               // And extract the original row.

        }

        public void Sort4()

        {

            var sort2 = _rows.OrderBy(x => x.Values[8], new  DummyComparer<double>() ).ToArray();

        }

        public void Sort5()

        {

            var sort2 = _rows.OrderBy(r => r, new DummyComparer<Row>() ).ToArray();

        }

    }

    static TimeSpan Time(Action action, int count)

    {

        var stopwatch = new System.Diagnostics.Stopwatch();

        stopwatch.Start();

        try

        {

            for (int i = 0; i < count; i++)

                action();

        }

        finally

        {

            stopwatch.Stop();

        }

​

        return stopwatch.Elapsed;

    }   

    static void Main(string[] args)

    {

        int count = 100;

        var sort = new Sort();

        sort.Sort1();

        sort.Sort2();

        sort.Sort3();

        var elapsed1 = Time(() => sort.Sort1(), count);

        var elapsed2 = Time(() => sort.Sort2(), count);

        var elapsed3 = Time(() => sort.Sort3(), count);

​

        Console.WriteLine("Average time per repetition for {0} reps of Sort1: {1:0.0000} ms.", count, elapsed1.TotalMilliseconds/((double)count));

        Console.WriteLine("Average time per repetition for {0} reps of Sort2: {1:0.0000} ms ({2:0.00}% slower).", count, elapsed2.TotalMilliseconds/((double)count), -100.0*(elapsed1 - elapsed2)/elapsed1);

        Console.WriteLine("Average time per repetition for {0} reps of Sort3: {1:0.0000} ms ({2:0.00}% slower).", count, elapsed3.TotalMilliseconds/((double)count), -100.0*(elapsed1 - elapsed3)/elapsed1);

        try

        {

            sort.Sort4();

        }

        catch (Exception ex)

        {

            Console.WriteLine("\nTraceback for _rows.OrderBy(x => x.Values[8]).ToArray():");

            Console.WriteLine(ex);

        }

        try

        {

            Console.WriteLine("\n_rows.OrderBy(e => e, comparer).ToArray():");

            sort.Sort5();

        }

        catch (Exception ex)

        {

            Console.WriteLine(ex);

        }

        Console.WriteLine(Comparer<double>.Default);

    }

}

​