title: Flatten all values of multiple arrays in Swift
body: <p>I have a Dictionary of Integer Arrays like below:</p>
  
  <p><code>let numbers = [1: [2, 3], 4: [5, 6, 7], 8: [9]]</code></p>
  
  <p>What I really want is a single flattened Array of all of the values (which themselves are arrays), like so:</p>
  
  <p><code>[2, 3, 5, 6, 7, 9]</code></p>
  
  <p>Now, I have been able to call <code>numbers.values.array</code> to get:</p>
  
  <p><code>[[2, 3], [5, 6, 7], [9]]</code></p>
  
  <p>But what I'm looking for is to merge these one step further, flattening them.</p>
  
  <p>Does Swift (1.1, or 1.2) offer a convenience method for this?</p>