title: Selecting a random element for a specific key in a Multimap
body: <p>How can I select a random element for a specific keys in a multimap. For example:</p>
  
  <pre><code>multimap&lt;string, string&gt; map;
  map.insert(pair&lt;string, string&gt;("Mammal", "Tiger"));
  map.insert(pair&lt;string, string&gt;("Mammal", "Chicken"));
  map.insert(pair&lt;string, string&gt;("Mammal", "Fox"));
  map.insert(pair&lt;string, string&gt;("Fish", "Clown Fish"));
  map.insert(pair&lt;string, string&gt;("Fish", "Ray"));
  </code></pre>
  
  <p>In the above, what would be the best way to get a random "Mammal"?</p>
  
  <p>I know I can get the iterators for the "Mammal" so:</p>
  
  <pre><code>pair&lt;MultiMapIt,MultiMapIt&gt;iterators = mMultiMap.equal_range("Mammal");
  // loop through each... and select one.
  </code></pre>
  
  <p>But I am sure there is a better solution... perhaps using the iterator as numbers..<br>
  Thanks</p>