README

🔥 Recommendations for PHP using collaborative filtering

• Supports user-based and item-based recommendations
• Works with explicit and implicit feedback
• Uses high-performance matrix factorization

Installation

Run:

composer require ankane/disco

Add scripts to composer.json to download the shared library:

    "scripts": {
        "post-install-cmd": "Disco\\Library::check",
        "post-update-cmd": "Disco\\Library::check"
    }

And run:

composer install

Getting Started

Create a recommender

use Disco\Recommender;

$recommender = new Recommender();

If users rate items directly, this is known as explicit feedback. Fit the recommender with:

$recommender->fit([
    ['user_id' => 1, 'item_id' => 1, 'rating' => 5],
    ['user_id' => 2, 'item_id' => 1, 'rating' => 3]
]);

IDs can be integers or strings

If users don’t rate items directly (for instance, they’re purchasing items or reading posts), this is known as implicit feedback. Leave out the rating.

$recommender->fit([
    ['user_id' => 1, 'item_id' => 1],
    ['user_id' => 2, 'item_id' => 1]
]);

Each user_id/item_id combination should only appear once

Get user-based recommendations - “users like you also liked”

$recommender->userRecs($userId);

Get item-based recommendations - “users who liked this item also liked”

$recommender->itemRecs($itemId);

Use the count option to specify the number of recommendations (default is 5)

$recommender->userRecs($userId, count: 3);

Get predicted ratings for specific users and items

$recommender->predict([['user_id' => 1, 'item_id' => 2], ['user_id' => 2, 'item_id' => 4]]);

Get similar users

$recommender->similarUsers($userId);

Examples

MovieLens

Load the data

use Disco\Data;

$data = Data::loadMovieLens();

Create a recommender and get similar movies

$recommender = new Recommender(factors: 20);
$recommender->fit($data);
$recommender->itemRecs('Star Wars (1977)');

Storing Recommendations

Save recommendations to your database.

Alternatively, you can store only the factors and use a library like pgvector-php. See an example.

Algorithms

Disco uses high-performance matrix factorization.

• For explicit feedback, it uses stochastic gradient descent
• For implicit feedback, it uses coordinate descent

Specify the number of factors and epochs

new Recommender(factors: 8, epochs: 20);

If recommendations look off, trying changing factors. The default is 8, but 3 could be good for some applications and 300 good for others.

Validation

Pass a validation set with:

$recommender->fit($data, validationSet: $validationSet);

Cold Start

Collaborative filtering suffers from the cold start problem. It’s unable to make good recommendations without data on a user or item, which is problematic for new users and items.

$recommender->userRecs($newUserId); // returns empty array

There are a number of ways to deal with this, but here are some common ones:

• For user-based recommendations, show new users the most popular items.
• For item-based recommendations, make content-based recommendations.

Reference

Get ids

$recommender->userIds();
$recommender->itemIds();

Get the global mean

$recommender->globalMean();

Get factors

$recommender->userFactors($userId);
$recommender->itemFactors($itemId);

Credits

Thanks to LIBMF for providing high performance matrix factorization

History

View the changelog

Contributing

Everyone is encouraged to help improve this project. Here are a few ways you can help:

• Report bugs
• Fix bugs and submit pull requests
• Write, clarify, or fix documentation
• Suggest or add new features

To get started with development:

git clone https://github.com/ankane/disco-php.git
cd disco-php
composer install
composer test