# 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.

```csharp label="C#"
await _feedsV3Client.CreateFeedGroupAsync(new CreateFeedGroupRequest
{
    ID = "myid",
    ActivitySelectors = new List<ActivitySelectorConfig>
    {
        new() { Type = "following" }
    },
    Ranking = new 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/dotnet-csharp/activity-processors/) or by [setting the `interest_tags` field](https://getstream.io/activity-feeds/docs/dotnet-csharp/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/dotnet-csharp/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.

```csharp label="C#"
await _feedsV3Client.GetOrCreateFeedAsync("timeline", "john", new GetOrCreateFeedRequest
{
    UserID = "john",
    InterestWeights = new Dictionary<string, double>
    {
        ["travel"] = 1.0,
        ["food"] = 0.5,
        ["exercise"] = -1.0
    }
});
```

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/dotnet-csharp/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:

```csharp label="C#"
// Using preference_score with expression type
await _feedsV3Client.CreateFeedGroupAsync(new CreateFeedGroupRequest
{
    ID = "myid",
    ActivitySelectors = new List<ActivitySelectorConfig>
    {
        new() { Type = "following" }
    },
    Ranking = new RankingConfig
    {
        Type = "expression",
        Score = "preference_score * popularity"
    }
});

// Using preference_score with interest type
await _feedsV3Client.CreateFeedGroupAsync(new CreateFeedGroupRequest
{
    ID = "myid_interest",
    ActivitySelectors = new List<ActivitySelectorConfig>
    {
        new() { Type = "following" }
    },
    Ranking = new RankingConfig
    {
        Type = "interest",
        Score = "preference_score * interest_score * popularity"
    }
});
```

See [Activity feedback](https://getstream.io/activity-feeds/docs/dotnet-csharp/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/dotnet-csharp/interest-ranking/](https://getstream.io/activity-feeds/docs/dotnet-csharp/interest-ranking/).