> ## Documentation Index
> Fetch the complete documentation index at: https://algolia.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Index strings as numeric attributes

> Learn how to index numeric variation to a string attribute

In some situations,
it makes sense to index a numeric representation of a string attribute,
for example for sorting by clothing size.
Size is usually a string (S, M, L, etc),
but sorting alphabetically will yield strange results (S, L, M).
It makes sense to replace these values with a numeric attribute to sort.

It's possible to add a new attribute containing this value by implementing a custom observer.
To make changes to the attributes being indexed, observe the [`algolia_after_create_product_object`](/doc/integration/magento-2/customize/custom-back-end-events#dispatched-after-fetching-products-attributes-for-indexing) event with a custom observer.

<Info>
  This tutorial assumes knowledge of writing a custom observer.
  For more information, see [Create a custom extension](/doc/integration/magento-2/guides/create-a-custom-extension).
</Info>

## Create observer

Create the `Observer/TransformAttribute.php` file, and add a new Observer class in it.

```php PHP icon=code theme={"system"}
namespace Algolia\CustomAlgolia\Observer;

use Magento\Framework\Event\Observer;
use Magento\Framework\Event\ObserverInterface;

class TransformAttribute implements ObserverInterface
{
  public function execute(Observer $observer)
  {
    $record = $observer->getData('custom_data');

    // $sizes = ['S', 'M', 'L'];
    $sizes = $record['sizes'];

    // S => 1, M => 2, L => 3
    $replacementNumbers = [1, 2, 3];

    $record['numeric_sizes'] = array_replace($sizes, $replacementNumbers);
  }
}
```

Modify the code in the `execute` block as needed.
In this example, the clothing sizes are transformed into numeric values.

## Register the observer

To register your observer,
add the following snippet to the [`etc/events.xml`](https://github.com/algolia/algoliasearch-custom-algolia-magento-2/blob/master/etc/events.xml) file:

```xml XML icon=code-xml theme={"system"}
<event name="algolia_after_create_product_object">
    <observer name="customalgolia_transform_attribute" instance="Algolia\CustomAlgolia\Observer\TransformAttribute" />
</event>
```

## Reindex data

With the custom observer in place, the catalog needs to be [reindexed](/doc/integration/magento-2/how-it-works/indexing) for the changes to take effect.