# Interest ranking

Interest weights help customize the ranking to users' interests. If you want to create a ranking expression that relies on interest weights, use `interest` type ranking.

```php label="PHP"
$createResponse = $feedsClient->createFeedGroup(
  new GeneratedModels\CreateFeedGroupRequest(
      id: "myid",
      activitySelectors: [
          new GeneratedModels\ActivitySelectorConfig(
              type: 'following'
          )
      ],
      ranking: new GeneratedModels\RankingConfig(
          type: 'interest',
          score: 'interest_score * popularity',
      )
  )
);
```

`interest_score` is computed by combining activity topics and the specific user's interests. Each of the activity's `interest_tags` that matches one of the user's interests adds half of that interest's weight, and the total is clamped to between -1 and 1. A single matching tag with weight `1.0` gives `0.5`, and tags with a weight of `0` or below pull the score down. The score is `0` when the activity has no `interest_tags` or none of them match. `interest_score` is only computed with `interest` type ranking; with `expression` ranking it is always `0`.

## Activity topics

The topic of an activity can be computed automatically using [activity processors](https://getstream.io/activity-feeds/docs/php/activity-processors/) or by [setting the `interest_tags` field](https://getstream.io/activity-feeds/docs/php/activities/#overview-of-all-activity-fields) via the Stream API.

## User interests

A user's interests are computed automatically by the Stream API from the `interest_tags` on activities the user has reacted to, directly or through a comment. Recent reactions count more: each reaction's contribution halves every 30 days. The user's strongest computed tag has weight `1.0`, and the other computed tags get a proportional weight between 0 and 1. When ranking with `interest` type, the top five tags with a positive weight are used, plus every tag with a weight of `0` or below as a penalty. You can also seed and manage a user's interests yourself, see the [User interests](https://getstream.io/activity-feeds/docs/php/user-interests/) guide.

You can also pass `interest_weights` when reading the feed. These weights are **merged** with the user's stored interests (computed and manual) rather than replacing them:

- Tags that appear only in the stored interests or only in `interest_weights` both contribute to `interest_score`.
- If the same tag appears in both, the value from `interest_weights` is used (an explicit override for that tag).
- If you omit `interest_weights` or pass an empty map, ranking uses only the user's stored interests.
- Set `overwrite_interest_weights: true` to replace the stored interests with `interest_weights` for that request instead of merging. The flag has no effect when `interest_weights` is empty.

```php label="PHP"
$feedResponse = $feedsClient->feed('timeline', 'john')->getOrCreateFeed(
  new GeneratedModels\GetOrCreateFeedRequest(
      interestWeights: [
          'travel' => 1.0,
          'food' => 0.5,
          'exercise' => -1.0
      ],
      userID: "john"
  )
);
```

Use interest weights between -1 and 1, where 1 means a user is very interested in a topic and -1 means they dislike it. Values outside this range are not rejected, but `interest_score` is still clamped to between -1 and 1.

## Preference score

`preference_score` reflects how much an activity matches the user's preferences based on [activity feedback](https://getstream.io/activity-feeds/docs/php/activity-feedback/) (show more/less). For each of the activity's `interest_tags`, it counts the user's show-more votes minus show-less votes on that tag, divides the total by 3 and clamps it to between -1 and 1. It is `0` when the activity has no `interest_tags` or the user has given no feedback on them.

In the `foryou` feed group, activities whose `interest_tags` have collected strong negative feedback are also removed from the feed: at least 3 show-less votes on the activity's tags with more show-less than show-more votes, or a net of 3 or more show-less votes. Other feed groups don't remove activities based on show more/less feedback, but can still use `preference_score`.

You can use `preference_score` in your ranking expressions with both `expression` and `interest` type ranking to boost activities that match user preferences:

```php label="PHP"
// Using preference_score with expression type
$createResponse = $feedsClient->createFeedGroup(
  new GeneratedModels\CreateFeedGroupRequest(
      id: "myid",
      activitySelectors: [
          new GeneratedModels\ActivitySelectorConfig(
              type: 'following'
          )
      ],
      ranking: new GeneratedModels\RankingConfig(
          type: 'expression',
          score: 'preference_score * popularity',
      )
  )
);

// Using preference_score with interest type
$createResponse = $feedsClient->createFeedGroup(
  new GeneratedModels\CreateFeedGroupRequest(
      id: "myid_interest",
      activitySelectors: [
          new GeneratedModels\ActivitySelectorConfig(
              type: 'following'
          )
      ],
      ranking: new GeneratedModels\RankingConfig(
          type: 'interest',
          score: 'preference_score * interest_score * popularity',
      )
  )
);
```

See [Activity feedback](https://getstream.io/activity-feeds/docs/php/activity-feedback/) for more information on how users can provide feedback that affects `preference_score`.

---

For the most recent version of this documentation, visit [https://getstream.io/activity-feeds/docs/php/interest-ranking/](https://getstream.io/activity-feeds/docs/php/interest-ranking/).