Sort and merge list based on another list

Here I'm merging a list to end of another list after sorting it according to another list.This should sort processdetails list according to the order in routeplans list if any item not present in processdetails list is found it should keep the order and add it to processdetails list. Simply saying it just merging two lists based on another list.The below code works fine, I want to know whether there is cleaner way of doing this.if possible in linq.

```
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SortByList
{
public class OnGoingProcess
{
public long Id { get; set; }

public string Name { get; set; }
public string Code { get; set; }
}

class Program
{
static void Main(string[] args)
{
var processDetails = new List();
processDetails.Add(new OnGoingProcess() { Id = 120, Name = "Process 29", Code = "T20" });
processDetails.Add(new OnGoingProcess() { Id = 100, Name = "Process 2", Code = "A20" });
processDetails.Add(new OnGoingProcess() { Id = 99, Name = "Process 3", Code = "S20" });
processDetails.Add(new OnGoingProcess() { Id = 85, Name = "Process 229", Code = "B20" });
processDetails.Add(new OnGoingProcess() { Id = 220, Name = "Process 39", Code = "C20" });
processDetails.Add(new OnGoingProcess() { Id = 15, Name = "Process 20", Code = "D20" });
processDetails.Add(new OnGoingProcess() { Id = 101, Name = "Process 129", Code = "G20" });

var routePlans = new List();
routePlans.Add(new OnGoingProcess() { Id = 100, Name = "Process 2" });
routePlans.Add(new OnGoingProcess() { Id = 120, Name = "Process 29" });
routePlans.Add(new OnGoingProcess() { Id = 222, Name = "Process new" });
routePlans.Add(new OnGoingProcess() { Id = 85, Name = "Process 229" });
routePlans.Add(new OnGoingProcess() { Id = 101, Name = "Process 129" });

var sortedPlans = new List();

Very poor problem statement. Problem statement is based on your perceived solution so review is difficult. I could only figure out what you are trying to do by reviewing the code.

Why long Id? If you have that many OnGoingProcess then will probably need a different approach.

Have proper constructors for OnGoingProcess and make Id read only.

Create a proper application and test. Don't just jam everything in Main.

You are changing selectedDetails. A calling procedure does not want an input changed. Output a new List mergedDetails.

Proper problem statement

processDetails and sortedPlans are each List of OnGoingProcess identified by property Id

Need output in this order

-
processDetails not present in sortedPlans (in the order in processDetails)

-
sortedPlans (in the order of sortedPlans)

if present in processDetails then processDetails

else then sorted plan

Putting those thoughts in action

public static void OnGoingProcessMergeTest()
{
    var processDetails = new List()
    { new OnGoingProcess(120, "Process 29", "T20"), new OnGoingProcess(100, "Process 2", "A20"), new OnGoingProcess(99, "Process 3", "S20"),
      new OnGoingProcess(85, "Process 229", "B20"), new OnGoingProcess(220, "Process 39", "C20"), new OnGoingProcess(15, "Process 20", "D20"),
      new OnGoingProcess(101, "Process 129", "G20")};

    var routePlans = new List()
    { new OnGoingProcess(100, "Process 2"), new OnGoingProcess(120,"Process 29"), new OnGoingProcess(222, "Process new"),
      new OnGoingProcess(85, "Process 229"), new OnGoingProcess(101, "Process 129")};

    List mergedDetails = OnGoingProcessMerge2(processDetails, routePlans);
    foreach (var sorted in mergedDetails)
    {
        Debug.WriteLine("Id : " + sorted.Id + " Name : " + sorted.Name + " Code : " + sorted.Code);
    }
    Debug.WriteLine("");
}       
public static List OnGoingProcessMerge2(List processDetails, List routePlans)
{
    List onGoingProcessMerge = processDetails.Where(x => !(routePlans.Any(y => y.Id == x.Id))).ToList();
    foreach(OnGoingProcess routePlan in routePlans)
    {
        OnGoingProcess processDetail = processDetails.FirstOrDefault(x => x.Id == routePlan.Id);
        onGoingProcessMerge.Add(processDetail ?? routePlan);
    }
    return onGoingProcessMerge;
}

StackExchange Code Review Q#151460, answer score: 2