title: Filter Map by key set
body: <p>Is there a shortcut to filter a Map keeping only the entries where the key is contained in a given Set?</p>
  
  <p>Here is some example code</p>
  
  <pre><code>scala&gt; val map = Map("1"-&gt;1, "2"-&gt;2, "3"-&gt;3)
  map: scala.collection.immutable.Map[java.lang.String,Int] = Map(1 -&gt; 1, 2 -&gt; 2, 3 -&gt; 3)
  
  scala&gt; map.filterKeys(Set("1","2").contains)
  res0: scala.collection.immutable.Map[java.lang.String,Int] = Map(1 -&gt; 1, 2 -&gt; 2)
  </code></pre>
  
  <p>I am searching for something shorter than this.</p>