title: "Grouping" dictionary by value
body: <p>I have a dictionary: <code>Dictionary&lt;int,int&gt;</code>. I want to get new dictionary where keys of original dictionary represent as <code>List&lt;int&gt;</code>. This is what I mean:</p>
  
  <pre><code>var prices = new Dictionary&lt;int,int&gt;();
  </code></pre>
  
  <p>The <code>prices</code> contain the following data:</p>
  
  <pre><code>1   100
  2   200
  3   100
  4   300
  </code></pre>
  
  <p>I want to get the <code>IList&lt;Dictionary&lt;int,List&lt;int&gt;&gt;&gt;</code>:  </p>
  
  <pre><code>int      List&lt;int&gt;
  100      1,3
  200      2
  300      4
  </code></pre>
  
  <p>How can I do this?  </p>