title: Array diff of specific key within multi-dimensional array
body: <p>I have two arrays of products, both formatted exactly the same, like so:</p>
  
  <pre><code>$products = array(
      [0] =&gt; array(
          ['product_id'] =&gt; 33
          ['variation_id'] =&gt; 0
          ['product_price'] =&gt; 500.00
      ),
      [1] =&gt; array(
          ['product_id'] =&gt; 48
          ['variation_id'] =&gt; 0
          ['product_price'] =&gt; 600.00
      ),
  )
  </code></pre>
  
  <p>I would like to be able to return a list of only those products not found in the second array, based on the product ID. </p>
  
  <p>I only care about those NOT found in the second array, not additional ones added to the first, so array_diff won't seem to do the trick.</p>