Acf

A lightweight recommender engine for implicit feedback datasets

The package implements an algorithm described in Collaborative Filtering for Implicit Feedback Datasets paper. The algorithm is based on the following ideas:

• using collaborative filtering with latent factors
• transforming feedback observations into binary preferences with associated confidence levels
• using alternating least sqaures to compute the matrix factorization

Install

The package requires Python 3.7 or newer, the only dependencies are numpy and pandas. To install it, run

pip install acf

Usage

The following example shows how to train a model and compute predictions.

import acf
import pandas as pd

# assuming the data are in the following format:
# | user_id | item_id | feedback |
# |---------|---------|----------|
# | 2491    | 129     | 2        |

interactions = pd.read_csv('interactions.csv')

engine = acf.Engine(reg_lambda=1, alpha=35, n_factors=2, random_state=0)

engine.fit(interactions,
           user_column='user_id',
           item_column='item_id',
           feedback_column='feedback',
           n_iter=20,
           n_jobs=4)

# get the best 20 recommendations
prediction = engine.predict(user=2491, top_n=20)

# to print training loss value at every iteration
print(engine.loss)

Model Evaluation

For performance evaluation, the package offers metrics.mean_rank function that implements "mean rank" metric as defined by equation 8 in the paper.

The metric is a weighted mean of percentile-ranked recommendations (rank_ui = 0 says that item i is the first to be recommended for user u and item j with rank_uj = 1 is the last to be recommended) where the weights are the actual feedback values from R user-item matrix.

interactions_test = pd.read_csv('intercations_test.csv')

print(acf.metrics.mean_rank(interactions=interactions_test,
                            user_column='user_id',
                            item_column='item_id'
                            feedback_column='feedback',
                            engine=engine))

Model Persistence

Trained model can be serialized and stored using joblib or pickle.

To store a model:

with open('engine.joblib', 'wb') as f:
    joblib.dump(engine, f)

To load a model:

with open('engine.joblib', 'rb') as f:
    engine = joblib.load(f)

Public API

acf.Engine

acf.core.computation.Engine(reg_lambda=0.1, alpha=40,
                            n_factors=10, random_state=None):

Class exposing the recommender.

• reg_lambda: regularization strength
• alpha: gain parameter in feedback-confidence transformation c_ui = 1 + alpha * r_ui
• n_factors: number of latent factors
• random_state: initial RNG state

Properties:

• user_factors: user factor matrix
• item_factors: item factor matrix
• loss: training loss history

Methods:

Engine.fit(interactions, user_column, item_column,
           feedback_column, n_iter=20, n_jobs=1)

Trains the model.

• interactions: dataframe containing user-item feedbacks
• user_column: name of the column containing user ids
• item_column: name of the column containing item ids
• feedback_column: name of the column containing feedback values
• n_iter: number of alternating least squares iteration
• n_jobs: number of parallel jobs

Engine.predict(user, top_n=None)

Predicts the recommendation.

• user: user identification for whom the prediction is computed
• top_n: if not None, only the besr n items are included in the result

Returns: predicted recommendation score for each item as pandas.Series

acf.metrics.mean_rank

acf.core.metrics.mean_rank(interactions, user_column, item_column,
                           feedback_column, engine)

Computes mean rank evaluation.

• interactions: dataframe containing user-item feedbacks
• user_column: name of the column containing user ids
• item_column: name of the column containing item ids
• feedback_column: name of the column containing feedback values
• engine: trained acf.Engine instance

Returns: computed value

Tests

Tests can be executed by pytest as

python -m pytest acf/tests