[Plugin: Woocommerce] Make a "Products per page" dropdown

Hi all, I am trying to setup a dropdown to sort the number of products per page and I cant seem to get the kinks worked out.

Here is what I have so far, but it doesn’t work and didnt know if someone knew of a workable solution?

function woocommerce_sortby_page() {

	if ('woocommerce_catalog_page_ordering'==$twelve)
  {
  add_filter('loop_shop_per_page', create_function('$cols', 'return 12;'));
  }
elseif ('woocommerce_catalog_page_ordering'==$sixteen)
  {
  add_filter('loop_shop_per_page', create_function('$cols', 'return 16;'));
  }
else
  {
  add_filter('loop_shop_per_page', create_function('$cols', 'return 4;'));;
  }
}

function woocommerce_catalog_page_ordering() {
?>
<form action="<?php 'woocommerce_sortby_page' ?>">
<select name="woocommerce-sort-by-columns">
<option value="<?php $twelve ?>">12</option>
<option value="<?php $sixteen ?>">16</option>
</select>
</form>
<?php
}

add_action( 'woocommerce_pagination', 'woocommerce_catalog_page_ordering', 20 );

Thanks in advance!