title: Get specific key value pair from multidimensional array
body: <p>I have the following array:</p>
  
  <pre><code>array(2) {
    [0] =&gt; array(3) {
      ["submission_id"] =&gt; int(28)
      ["date"] =&gt; string(22) "2010-10-18 15:55:33+02"
      ["user_id"] =&gt; int(12)
    }
    [1] =&gt; array(3) {
      ["submission_id"] =&gt; int(37)
      ["date"] =&gt; string(22) "2010-11-21 16:02:07+01"
      ["user_id"] =&gt; int(23)
    }
  </code></pre>
  
  <p>I want to get only the user_id key values from this array. I could obviously loop over it, but I was wondering if there was a quicker way.</p>