title: Scala: join an iterable of strings
body: <p>How do I "join" an iterable of strings by another string in Scala?</p>
  
  <pre><code>val thestrings = Array("a","b","c")
  val joined = ???
  println(joined)
  </code></pre>
  
  <p>I want this code to output <code>a,b,c</code> (join the elements by ",").</p>