title: C#: Gets unmatched elements between 2 collections with Linq & Lambda
body: <p>I have two collections, compare them and want to get the unmatched items and put into a new collection. I don't want to use conventional method using 2 foreach loop. How to implement it using linq and lambda expression?
  e.g.</p>
  
  <pre><code>    int[] collection1 = new int[] { 1, 2, 3, 4, 5 };
      int[] collection2 = new int[] { 2, 3 };
      // Goal: Using Linq and Lambda Expression: the new collection3 should contain 1, 4, 5
  </code></pre>
  
  <p>Edited: sorry I forget to mention: collection2 is a subset of collection1, therefore all elements in collection2 must exist in collection1.</p>