Sort Products by popularity count in Magento

Advance shorting option for category/list page in magento
Note: Please Make  folder structure app/code/local  and place all files in same structure in this folder ,If you make changes in core files its your risk.please make proper backup for core files if you modify that .


Step -1.
For Advance shorting option you have to create new collection by overriding Collection class.Overrride the collection class(/app/code/core/Mage/Catalog/Model/Resource/Product/collection.php and create a new function

<?php 

public function sortByReview($dir){
 $table = $this->getTable('review/review');
 $entity_code_id = Mage::getModel('review/review')->getEntityIdByCode(Mage_Rating_Model_Rating::ENTITY_PRODUCT_CODE); 

 $cond = $this->getConnection()->quoteInto('t2.entity_pk_value = e.entity_id and ','').$this->getConnection()->quoteInto('t2.entity_id = ? ',$entity_code_id); 

 $this->getSelect()->joinLeft(array('t2'=>$table), $cond,array('review' => new Zend_Db_Expr('count(review_id)'))) 

->group('e.entity_id')->order("review $dir"); 

 }

 ?>

Step-2 Find the file config.php(/app/code/core/Mage/Catalog/Model/config.php) and search for    getAttributeUsedForSortByArray(), And add here search option name  you get an array which you want to show in  toolbar drop-down in product-listing  page in your magento store.(line 4)

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<?php public function getAttributeUsedForSortByArray() { $options = array( 'popularity' => Mage::helper('catalog')->__('Popularty'), 'topsellings' => Mage::helper('catalog')->__('Top Selling')  ); foreach ($this->getAttributesUsedForSortBy() as $attribute) { /* @var $attribute Mage_Eav_Model_Entity_Attribute_Abstract */ $options[$attribute->getAttributeCode()] = $attribute->getStoreLabel(); } return $options; } ?>

Step:3 Finally call overridden collection(created onStep-1) when Popularity attribute  (created on step 2) selected for sorting in list page. for this find 

/app/code/core/Mage/Catalog/Block/Product/List /toolbar.php
and include these lines.(line no..11 to 17) in setCollection method.

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<?php 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; }?>

Now you can see popularity option working in product listing page.