title: Grouping and summing a list into a map using Lambda
body: <p>I have a list of <code>MoveTrack</code> objects that i want to group by Month and count and store the data in a <code>Map&lt;String, Double&gt;</code>. I am trying to learn Lambda and experiment with it so trying to do this task with Lambda.</p>
  
  <pre><code>class MoveTrack {
  private Date time;
  private Double movementAmount;
  
  //getters and setters
  }
  
  // in my main method
  List&lt;MoveTrack&gt; mveTracking = new ArrayList&lt;&gt;();
  Map&lt;String, Double&gt; movMap = new HashMap&lt;&gt;();
  </code></pre>
  
  <p>So I want to be able to group the <code>moveTracking</code> list and sum the values into the <code>movMap</code>, with each Map Key = Month Name (January, February, etc.) and corresponding Value the movement amount which is a sum of doubles for that month.</p>