Inserting custom data to the_post() during loop

Question

I have some posts on my WordPress site, and let's say I want to add a random number for each post with $num as key and random() as value. Then I want to access them with something like:

$post->num or post_num()

Can this be done during The Loop? Since the value will change every time it is executed, I need to make it during The Loop. I can't add this random number as a custom field.

Is there a way to achieve this?

Answer 1

Yep, it's not very common, but perfectly viable and nifty technique.

After the posts are retrieved in WP_Query they are passed through the_posts filter like this (where $this is WP_Query instance):

$this->posts = apply_filters_ref_array( 'the_posts', array( $this->posts, &$this ) );

You just loop through array and assign the extra data you need to objects. Don't forget to check the query for being right query you want to target.