title: Remove all elements from array that do not start with a certain string
body: <p>I have an array that looks like this:</p>
  <pre><code>array(
    'abc' =&gt; 0,
    'foo-bcd' =&gt; 1,
    'foo-def' =&gt; 1,
    'foo-xyz' =&gt; 0,
    // ...
  )
  </code></pre>
  <p>How can I retain only the elements that start with <code>foo-</code>?</p>