What did you want to list from the users?

I want to filter the river only for users that have "New York" set as metadata "location" field, for example. Have I explained more clearly? 

Oh ok, you pretty much want to limit each user's river based on location. Something like a local feed right?

No I'm sorry, that was an example. I want to add a tab in activity page (one more than all, mine, following) in which I list only river activity of users with "Premium" value for "profile_type" field. I'm sorry if I didn't explain very well!

Ohhhhh, so a filter tab where only premium members can see other premium members' activities?

There's a good discussion here:

https://elgg.org/discussion/view/2200450/how-to-combine-own-following-river-activity-tabs-into-one

You need to custom code this function into your elgg network. I don't know if there's a plugin for that.

I was thinking about using joins and wheres options to get subject_guids only with correct metastrings associated. Do you think this is a good idea? Any tip on this argument?

Hello,

I used this but it doesn't work. Any help? (If I remove joins and wheres it works)

$db = elgg_get_config('dbprefix');
    $name_id = elgg_get_metastring_id('profilo_tipo');
    
    $value1 = elgg_get_metastring_id('Pro');
    $value2 = elgg_get_metastring_id('Business');
    
    $options = array(
        'offset'     => 0,
        'limit'      => 20,
        'type' => 'object',
        'subtypes' => array('hjwall', 'izap_videos', 'blog'),
         'no_results' => '',
    );
   
       $options['joins'][] = "JOIN {$db}metadata md1 ON (rv.subject_guid = md1.entity_guid)";
    $options['joins'][] = "JOIN {$db}metadata md2 ON (rv.subject_guid = md2.entity_guid)";
    
    $options['wheres'][] = "md1.name_id = {$name_id}";
    $options['wheres'][] = "md2.name_id = {$name_id}";
    $options['wheres'][] = "md1.value_id = {$value1}";
    $options['wheres'][] = "md2.value_id = {$value2}";

$river = elgg_get_river($options);

I do not think you need two joins, one should be enough.

How about

$options['joins'] =array("JOIN {$db}metadata md ON rv.subject_guid = md.entity_guid");

$options['wheres'] = array(("md.name_id = {$name_id}"),("md.value_id = {$value1} OR  md.value_id = {$value2}"));

You can also search for the way this query is formulated in error_log and try it in phpMyAdmin to see what is wrong.

Thank you, it works fine!