How to filter Magento Loaded Collection? -

what best practice add filter loaded collection in magento? want hide items out of stocks , last updated date not within last 30 days.

i try create function hide products in front end, realize won’t affect total item counts loaded in pager. discovered _getproductcollection() might method can use can’t add filter onto it.

i’m still new magento guidances highly appreciated.

$collection = mage::getmodel('catalog/product')->getcollection(); $collection->addfieldtofilter( 'status', '1' ); $collection->addfieldtofilter( 'created_at',     array(         'lteq'=>$last_day     ) );     $collection->addfieldtofilter(     'updated_at',     array(         'gteq'=>$first_day     ) );