Merging product attributes in Magento

Another magento snippet. With this you can merge product attributes:

// create product collection
$collection = Mage::getModel('catalog/product')
    ->getCollection();
// filter by attribute code
$collection->addAttributeToFilter($attributeCode, $from);
// get all product ids...
$ids = $collection->getAllIds();
// ...and update them
Mage::getSingleton('catalog/product_action')
    ->updateAttributes($ids, [$attributeCode => $to], 0);

Don't forget to initialize the following variables:

• $attributeCode - the code of the attribute, eg color.
• $from - the attribute value id you want to merge from, eg 145 for Cyan.
• $to - the attribute value id you want to merge to, eg 146 for Blue.

After that, reindex and drop the old attribute value.