title: Compare 2-dimensional data sets based on a specified second level value
body: <p>I have an array containing rows of associative data.</p>
  <pre><code>$array1 = array(
      array('ITEM' =&gt; 1),
      array('ITEM' =&gt; 2),
      array('ITEM' =&gt; 3),
  );
  </code></pre>
  <p>I have a second array, also containing rows of associative data, that I would like to filter using the first array.</p>
  <pre><code>$array2 = array(
      array('ITEM' =&gt; 2),
      array('ITEM' =&gt; 3),
      array('ITEM' =&gt; 1),
      array('ITEM' =&gt; 4),
  );
  </code></pre>
  <p>This feels like a job for <code>array_diff()</code>, but how can I compare the rows exclusively on the deeper <code>ITEM</code> values?</p>
  <p>How can I filter the second array and get the following result?</p>
  <pre><code>array(3 =&gt; array('ITEM' =&gt; 4))
  </code></pre>