title: C# LINQ Select objects with the same value of one property join values of other
body: <p>I have a list of prods like this:</p>
  
  <pre><code>Prod1: Id=1, Name="name1", Color="Blue"
  Prod2: Id=1, Name="name1", Color="Green"
  Prod3: Id=2, Name="Test2, Color="Red"
  </code></pre>
  
  <p>What I want to perform is to get reduced list like this:</p>
  
  <pre><code>Prod1: Id=1, Name="name1", Color="Blue, Green"
  Prod3: Id=2, Name="Test2, Color="Red"
  </code></pre>
  
  <p>I always want to take prods with the same id and add up their colors. I feel there is a clever one code line way to do this, but I somehow got stuck with:</p>
  
  <pre><code>productList.GroupBy(p =&gt; new { p.Id }).Select(x =&gt; x.First()).ToList();
  </code></pre>
  
  <p>which does not give me an ability to add second color. Will apreciate any help</p>