title: How to get a scala Map value, when the key is a tuple in which only the first element is known?
body: <p>Suppose I have a scala immutable <code>Map[(String, Boolean), Set[String]]</code>, e.g.:</p>
  
  <pre><code>val myMap = Map(("a",true) -&gt; Set("b","c"))
  </code></pre>
  
  <p>Now suppose I only know the first element of the key tuple, <code>"a"</code>. Can (and how if yes) I get the map's value for this key if:</p>
  
  <p>1) I <em>know</em> that the key could either be <code>("a", true)</code> or <code>("a", false)</code> (there cannot be two keys with the same String as the first element)</p>
  
  <p>2) I <em>don't know</em> that, in which case I wish to get some kind of concatenation on the possible two values, such as <code>v1.union(v2)</code> or <code>v1 ++ v2</code>, etc.</p>
  
  <p>Is there any scala "magic" I could use, like <code>myMap.get(("a", Any))</code>?</p>