Magento change Multiple select to dropdown with select all option in Advanced search

How to change Multiple select to dropdown with select all option in Advanced search - Magento.

Simply change statement in ... Mage/Block/Advanced/Form.php around line 207 (Magento 1.7)

if (is_array($options) && count($options)>2)

to any number higher than the number of your attribute options:

if (is_array($options) && count($options)>10000000)

Example:

Original code:

if (is_array($options) && count($options)>2) {
            $extra = 'multiple="multiple" size="4"';
            $name.= '[]';
        }
        else {
            array_unshift($options, array('value'=>'', 'label'=>Mage::helper('catalogsearch')->__('All')));
        }

My code:

if (is_array($options) && count($options)>50) {
            $extra ='multiple="multiple" size="4"';
            $name.= '[]';
        }
        else {
            array_unshift($options, array('value'=>'', 'label'=>Mage::helper('catalogsearch')->__('Select all')));
        }

My code, with dropdown option:

if (is_array($options) && count($options)>50) {
            $extra = array();
            $name.= '[]';
        }
        else {
            array_unshift($options, array('value'=>'', 'label'=>Mage::helper('catalogsearch')->__('Select all')));
        }