Sorting a list based on the contents of another list

Question

I have a list that contains a list of integers and another list that contains a class that holds both an integer and a string.

What I'm trying to do is sort my list alphabetically, putting the entries that exist in the first list first. Here is my code and expected output:

using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
    public static void Main()
    {
        var myList = new List<int>();
        myList.Add(5);
        myList.Add(15);

        var myclasses = new List<MyClass>();
        myclasses.Add(new MyClass {MyId = 8, MyString = "Entry1"});
        myclasses.Add(new MyClass {MyId = 12, MyString = "Entry2"});
        myclasses.Add(new MyClass {MyId = 1, MyString = "Entry3"});
        myclasses.Add(new MyClass {MyId = 15, MyString = "Entry4"});
        myclasses.Add(new MyClass {MyId = 9, MyString = "Entry5"});
        myclasses.Add(new MyClass {MyId = 5, MyString = "Entry6"});

        foreach (MyClass c in myclasses.OrderBy(z => myList.Contains(z.MyId)).ThenBy(z => z.MyString )) {
            Console.WriteLine("{0} ==> {1}", c.MyId, c.MyString);
        }

        // I'm expecting this output:
        //
        // 15 ==> Entry4
        // 5 ==> Entry6
        // 8 ==> Entry1
        // 12 ==> Entry2
        // 1 ==> Entry3
        // 9 ==> Entry5
    }

    public class MyClass {
        public int MyId { get; set; }
        public string MyString { get; set; }
    }
}

As you can see from my expected output, I want Entry6 and Entry4 to appear first since they appear in the first list. Then I just want an alphabetical list. I thought my LINQ statement would be correct, but its not giving me the correct results. Any help would be appreciated.

Answer 1

Simply invert the myList.Contains condition:

foreach (MyClass c in myclasses.OrderBy(z => !myList.Contains(z.MyId)).ThenBy(z => z.MyString )) {
       Console.WriteLine("{0} ==> {1}", c.MyId, c.MyString);
}

I believe it's because of the true is treated as 1 while false is 0.

Answer 2

Use this:

myclasses.OrderBy(z => !myList.Contains(z.MyId)).ThenBy(z => z.MyString)