title: loop through values of a nested map in a map
body: <p>I would be really grateful if you could help me with that. </p>
  
  <pre><code>Map&lt;String, Double&gt; movieMap = new HashMap&lt;String, Double&gt;;
  movieMap.add("MovieA", 3);
  movieMap.add("MovieB", 5);
  movieMap.add("MovieC", 4);
  movieMap.add("MovieD", 3.5);
  movieMap.add("MovieE", 2.5);
  
  Map&lt;String, Double&gt; movieMap2 = new HashMap&lt;String, Double&gt;;
  movieMap2.add("MovieA", 3.5);
  movieMap2.add("MovieB", 2.5);
  movieMap2.add("MovieC", 4.5);
  movieMap2.add("MovieD", 2);
              .
              .
              .
  Map&lt;String, Double&gt; movieMapi = new HashMap&lt;String, Double&gt;;
  movieMap2.add("MovieA", 5);
  movieMap2.add("MovieC", 1.5);
  movieMap2.add("MovieD", 2);
  
  Map&lt;String, Map&lt;String, Double&gt;&gt; userMap = new HashMap&lt;String, Map&lt;String, Double&gt;&gt;;
  userMap.add("Nick", movieMap);
  userMap.add("Bill", movieMap2);
             .
             .
             .
  userMap.add("Tom", movieMapi);
  </code></pre>
  
  <p>What i want to do is to make a function <em>compare(userA, userB)</em> and put the common movies and their rates into a new Map. By way of example the output of compare(Nick,Tom) should be a Map with keys - values : <strong>{{"MovieA", {5,3}}, {"MovieC", {4,1.5}}, {"MovieD", {3.5,2}}}</strong>  </p>
  
  <p>It seems pretty hard for me to solve it..Can you please help me?<br>
  Thanks...</p>