How to Set, Retrieve and Unset Session Variables in Magento

Set session Data

$session = Mage::getSingleton("core/session", array("name"=>"frontend"));

$session->setData("day_filter", 'weeks');
$session->setData("days", '5');          
$session->setData("next_delivery_date", '2012-05-12');

or

Mage::getSingleton('core/session')->setIsSalesrepTax('test'); 

UnSet session Data

$session->unsetData('day_filter');
$session->unsetData('days');
$session->unsetData('next_delivery_date'); 

$session->unsetData('IsSalesrepTax');  

Session Data Set to null

$session->setData('day_filter', NULL);
$session->setData('days', NULL);
$session->setData('next_delivery_date', NULL); 

Magento Set, Retrieve and Unset Session Variables

 To set a Magento session variable:

$myValue = 'My session';
Mage::getSingleton('core/session')->setMyValue($myValue);

To Retrieve:

$myValue=Mage::getSingleton('core/session')->getMyValue();

To Unset:

Mage::getSingleton('core/session')->unsMyValue();