// @nuget: BenchmarkDotNet -Version 0.13.2

​

using System;

using System.Collections.Generic;

using System.Linq;

using BenchmarkDotNet.Running;

using BenchmarkDotNet.Attributes;

using BenchmarkDotNet.Jobs;

using BenchmarkDotNet.Configs;

using BenchmarkDotNet.Toolchains.InProcess.Emit;

using BenchmarkDotNet.Loggers;

using Perfolizer.Horology;

​

[assembly: System.Diagnostics.Debuggable(isJITTrackingEnabled: false, isJITOptimizerDisabled: false)]

BenchmarkRunner.Run<BenchMarks>(DefaultConfig.Instance

        .AddJob(Job.Default

            .WithToolchain(new InProcessEmitToolchain(

                timeout: TimeSpan.FromSeconds(9), // timeout for .NET Fiddle

                logOutput: false)) // Intermediate logging

                .WithLaunchCount(1)

                .WithWarmupCount(10)

                .WithIterationCount(20)

                .WithIterationTime(TimeInterval.FromMilliseconds(100))

               )

        .AddLogger(new ConsoleLogger(unicodeSupport: true, ConsoleLogger.CreateGrayScheme())) // Color codes are not supported in .NET Fiddle

        .WithOptions(ConfigOptions.DisableLogFile));

​

public class Parent {

    public List<Child> Children { get; set; }

}

​

public class Child {

    public string Name { get; set; }

    public int Value { get; set; }

}

​

[MemoryDiagnoser(true)]

public class BenchMarks{

    public List<Parent> Parents { get; set; }

    [GlobalSetup]

    public void Setup()

    {

        Parents = new List<Parent>();

        for (var j = 0; j < 10; j++)

        {

            for (var i = 0; i < 500; i++)

            {

                Parents.Add(new Parent

                {

                    Children = new List<Child>

                    {

                        new Child

                        {

                            Name = j.ToString(),

                            Value = i

                        }

                    }

                });

            }

        }

    }

    [Benchmark]

    public void GetWithTwoForeach(){

        var dict = new Dictionary<string,int>();

        foreach(var parent in Parents){

            foreach(var child in parent.Children){

                if (dict.ContainsKey(child.Name))

                    dict[child.Name] += child.Value;

                else

                    dict.Add(child.Name, child.Value);

            }

        }

    }

    [Benchmark]

    public void GetWithOneForeach(){

        var dict = new Dictionary<string,int>();

        foreach(var child in Parents.SelectMany(p=>p.Children)){

            if (dict.ContainsKey(child.Name))

                dict[child.Name] += child.Value;

            else

                dict.Add(child.Name, child.Value);

        }

    }

    [Benchmark]

    public void GetWithGroupSum(){

        var childGroups = Parents.SelectMany(p=>p.Children).GroupBy(c => c.Name);   

        var dict = childGroups.ToDictionary(cg => cg.Key, cg => cg.Sum(child => child.Value));

    }

}