using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public void Main()

    {

        List<SomeObject> objects = new List<SomeObject>();

        objects = new List<SomeObject>()

        {new SomeObject{Name = "Rando Object 1", Id = 5, ValuePairs = new List<KeyPair>()

        {new KeyPair{Key = "TestKey1", Value = "TestValue1"}, new KeyPair{Key = "TestKey2", Value = "TestValue2"}}}, new SomeObject{Name = "Rando Object 2", Id = 5, ValuePairs = new List<KeyPair>()

        {new KeyPair{Key = "TestKey3", Value = "TestValue3"}, new KeyPair{Key = "TestKey4", Value = "TestValue4"}}}};

    }

​

    public List<SomeObject> MergeObj(List<SomeObject> someObjects)

    {

        var idList = someObjects.Select(x => x.Id).Distinct().ToList();

        var newSomeObjects = new List<SomeObject>();

        idList.ForEach(x =>

        {

            var newValuePairList = new List<KeyPair>();

            someObjects.Where(y => y.Id == x).ToList().ForEach(y =>

            {

                newValuePairList.AddRange(y.ValuePairs);

            });

            newSomeObjects.Add(new SomeObject{Id = x, ValuePairs = newValuePairList});

        });

        return newSomeObjects;

    }

}

​

public class SomeObject

{

    public string Name

    {

        get;

        set;

    }

​

    public int Id

    {

        get;

        set;

    }

​

    public List<KeyPair> ValuePairs

    {

        get;

        set;

    }

}

​

public class KeyPair

{

    public string Key

    {

        get;

        set;

    }

​

    public string Value

    {

        get;

        set;

    }

}