title: Generating Map from Map of Maps using Lambda in Java 8
body: <p>I have a Map of Maps in the format </p>
  
  <pre><code>Map &lt; Integer, Map &lt; String, Integer &gt;&gt;
  </code></pre>
  
  <p>If I have data in the format of </p>
  
  <pre><code>&lt;1&gt;, &lt;&lt; X, 11 &gt;, &lt; Y, 13 &gt;, &lt; Z, 15 &gt;&gt;
  &lt;2&gt;, &lt;&lt; X,12 &gt;, &lt; A, 23 &gt;, &lt; L, 41 &gt;&gt; 
  </code></pre>
  
  <p>How to process this using Java 8 lambda and generate the following <br/></p>
  
  <pre><code>&lt;1&gt;, &lt;[11, 13, 15]&gt;
  &lt;2&gt;, &lt;[12, 23, 41]&gt; 
  </code></pre>
  
  <p>That is generate another Map where the key is the key of the outer map and the value is a List of the values of the inner Map. I know how to do this in the regular way but I am looking at how this using Java 8 Lambda.</p>