C# LINQ Orderby - How does true/false affect orderby?
<p>I was studying a bit of LINQ ordering as I have a list of Ids, and I need to order them sequentially. However, there are certain ids that need to take precedence over the standard ordering.</p>

<p>Given this C# code (which can be pasted into <a href="https://dotnetfiddle.net/" rel="noreferrer">.NET Fiddle</a> to test) the ordering works as I need it to, but I don't understand why a not (<code>!</code>) operator on a contains is giving me the correct ordering?</p>

<p>My expected ordering output is (<code>5, 1, 2, 3, 4, 6, 7, 8, 9</code>).</p>

<p>If I have a <a href="https://msdn.microsoft.com/en-us/library/system.linq.enumerable.contains(v=vs.110).aspx" rel="noreferrer"><code>Contains</code></a> in my ordering, shouldn't it give ordering priority to the rows that returned true? Instead it appears to give ordering priority to rows that return false.</p>

<pre><code>using System.Linq;
using System;

public class Program
{
  public static void Main()
  {
    var numbersToFilterBy = new [] {5, 11, 20};

    var x = new [] {new XClass(){Id = 1}, new XClass(){Id = 9}, new XClass(){Id = 5}, new XClass(){Id = 3}, new XClass(){Id = 4}, new XClass(){Id = 2}, new XClass(){Id = 6}, new XClass(){Id = 8}, new XClass(){Id = 7}};

    var trueData = (from data in x
                   orderby !numbersToFilterBy.Contains(data.Id), data.Id
                    select data).ToList();

    foreach(var item in trueData){
        Console.WriteLine(item.Id);
  }
}

public class XClass{
    public int Id{get;set;}
  }
}
</code></pre>

<p>What is the explanation as to why this happens?</p>