Get specific key value pair from multidimensional array
<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>
