I'm getting all products with this code:
->addAttributeToSelect('*')
->addStoreFilter()
->setVisibility(Mage::getSingleton('catalog/product_visibility')->getVisibleInCatalogIds());
$collection->getSelect()->order('rand()');
$collection->getSelect()->limit(12);
and also I added this code to get products with "size" attribute.
->addAttributeToFilter('size', '13')
And now, I'm asking how can I do that with array. I mean getting products value of size = 13,14,15 like array