using System;

using System.Collections.Generic;

using System.Linq;

using System.Text.Json;

public class Program

{

    public static void Main()

    {

        var obj = new List<FileDiff>()

                {

                    new FileDiff

                    {

                        Name = "test1",

                        Included = new Diff<int> {Added = new HashSet<int> {1, 2}},

                        Excluded = new Diff<int> {Added = new HashSet<int> {1, 2}},

                        Existing = new Diff<int> {Added = new HashSet<int> {1, 2, 3}}

                    },

                    new FileDiff

                    {

                        Name = "test1",

                        Included = new Diff<int> {Added = new HashSet<int> {3, 4, 5}},

                        Excluded = new Diff<int> {Added = new HashSet<int> {11, 222}},

                        Existing = new Diff<int> {Added = new HashSet<int>()}

                    },

                    new FileDiff

                    {

                        Name = "equal to test1",

                        Included = new Diff<int> {Added = new HashSet<int> {1, 2}},

                        Excluded = new Diff<int> {Added = new HashSet<int> {1, 2}},

                        Existing = new Diff<int> {Added = new HashSet<int> {1, 2, 3}}

                    },

            };

        var obj2 = obj

            .GroupBy(f => new

            {

                f.Included,

                f.Excluded,

                f.Existing,

            })

            .Select(g => new FileDiff2

            {

                Names = g.Select(f => f.Name).ToArray(),

                Included = g.Key.Included,

                Excluded = g.Key.Excluded,

                Existing = g.Key.Existing,

            })

            .ToList();

        Console.WriteLine(JsonSerializer.Serialize<List<FileDiff2>>((List<FileDiff2>)obj2, new JsonSerializerOptions { WriteIndented = true  }));

    }

}

​

public class FileDiff

{

    public string Name { get; set; }

    public Diff<int> Included { get; set; }

    public Diff<int> Excluded { get; set; }

    public Diff<int> Existing { get; set; }

}

​

public class FileDiff2

{

    public string[] Names { get; set; }

    public Diff<int> Included { get; set; }

    public Diff<int> Excluded { get; set; }

    public Diff<int> Existing { get; set; }

}

​

public class Diff<T> : IEquatable<Diff<T>>

{

    public HashSet<T> Added { get; set; }

    public override int GetHashCode()

    {

        unchecked

        {

            int hash = 19;

            foreach (var foo in Added)

            {

                hash = hash * 31 + foo.GetHashCode();

            }

            return hash;

        }

    }

    public override bool Equals(object obj)

    {

        return this.Equals(obj as Diff<T>);

    }

​

    public bool Equals(Diff<T> other)

    {

        if (other == null)

            return false;

​

        return this.Added.SetEquals(other.Added);

    }

}