How to sort Magento products by popularity in frontend?

I have created a module to add a new option in 'sort by' dropdown box in the category page. the new option should show in each and every category page same as 'position' option which is already there. I want to add 'popularity' as an option. My Model class is executing and it's adding the option to the option array. But the block is not working. Please I need your help to find the issue in my code?

Here is the Block class

<?php
class Tal_Popularity_Block_Product_List_Toolbar extends Mage_Catalog_Block_Product_List_Toolbar{ public function setCollection($collection) { $this->_collection = $collection; $this->_collection->setCurPage($this->getCurrentPage()); // we need to set pagination only if passed value integer and more that 0 $limit = (int)$this->getLimit(); if ($limit) { $this->_collection->setPageSize($limit); } if($this->getCurrentOrder() == 'popularity'){ $this->_collection->sortByReview($this->getCurrentDirection()); } else if ($this->getCurrentOrder()) { $this->_collection->setOrder($this->getCurrentOrder(), $this->getCurrentDirection()); } return $this; }}

following is my config.xml

<?xml version="1.0" ?> <config> <modules> <Tal_Popularity> <version>0.1.0</version> </Tal_Popularity> </modules> <frontend> <routers> <popularity> <use>standard</use> <args> <module>Tal_Popularity</module> <frontName>popularity</frontName> </args> </popularity> </routers> </frontend> <global> <models> <catalog> <rewrite> <config>Tal_Popularity_Model_Config</config> </rewrite> </catalog> </models> <blocks> <catalog> <rewrite> <product_list_toolbar>Tal_Popularity_Block_Product_List_Toolbar</product_list_toolbar> </rewrite> </catalog> <catalog> <rewrite> <catalog>Tal_Popularity_Block</catalog> </rewrite> </catalog> </blocks> <resources> <popularity_setup> <setup> <module>Tal_Popularity</module> </setup> <connection> <use>core_setup</use> </connection> </popularity_setup> <popularity_write> <connection> <use>core_write</use> </connection> </popularity_write> <popularity_read> <connection> <use>core_read</use> </connection> </popularity_read> </resources> </global> </config> <rewrite> <product_list_toolbar>Tal_Popularity_Block_Product_List_Toolbar</product_list_toolbar> </rewrite> </catalog> <catalog> <rewrite> <catalog>Tal_Popularity_Block</catalog> </rewrite> </catalog> </blocks> <resources> <popularity_setup> <setup> <module>Tal_Popularity</module> </setup> <connection> <use>core_setup</use> </connection> </popularity_setup> <popularity_write> <connection> <use>core_write</use> </connection> </popularity_write> <popularity_read> <connection> <use>core_read</use> </connection> </popularity_read> </resources> </global></config>