title: Java stream - Sort a List to a HashMap of Lists
body: <p>Let's say I have a <code>Dog</code> class. </p>
  
  <p>Inside it I have a <code>Map&lt;String,String&gt;</code> and one of the values is <code>Breed</code>.</p>
  
  <pre><code>public class Dog {
      String id;
      ...
      public Map&lt;String,String&gt;
  }
  </code></pre>
  
  <p>I want to get a <code>Map</code> of <code>List</code>s:</p>
  
  <pre><code>HashMap&lt;String, List&lt;Dog&gt;&gt; // breed to a List&lt;Dog&gt;
  </code></pre>
  
  <p>I'd prefer to use a <code>Stream</code> rather than iterating it.  </p>
  
  <p>How can I do it? </p>