Improved Recurrent Neural Networks for Session-based
Recommendations
Yong Kiam Tan
tanyongkiam@gmail.com
Xinxing Xu
xuxinx@ihpc.a-star.edu.sg
Yong Liu
liuyong@ihpc.a-star.edu.sg
Institute of High Performance Computing, A*STAR
1 Fusionopolis Way, Singapore 138632
ABSTRACT
Recurrent neural networks (RNNs) were recently proposed
for the session-based recommendation task. The models
showed promising improvements over traditional recommen-
dation approaches. In this work, we further study RNN-
based models for session-based recommendations. We pro-
pose the application of two techniques to improve model
performance, namely, data augmentation, and a method to
account for shifts in the input data distribution. We also
empirically study the use of generalised distillation, and a
novel alternative model that directly predicts item embed-
dings. Experiments on the RecSys Challenge 2015 dataset
demonstrate relative improvements of 12.8% and 14.8% over
previously reported results on the Recall@20 and Mean Re-
ciprocal Rank@20 metrics respectively.
CCS Concepts
•Computing methodologies → Supervised learning;
Neural networks; •Information systems → Recom-
mender systems;
Keywords
Recurrent neural networks; Recommender systems; Session-
based recommendations
1. INTRODUCTION
Users of e-commerce websites are often inundated by the
huge number of items available for sale. Recommender sys-
tems can be used to enhance user experience by making
personalized and useful recommendations for each user. For
example, the system could automatically display items of
interest, or suggest new discounts relevant to each user. In
order to personalize recommendations, traditional recom-
mender systems often need to build up a user profile. Col-
laborative filtering approaches [15, 14, 21] can define user-
user similarity based on their history of purchases, or they
Publication rights licensed to ACM. ACM acknowledges that this contribution was
authored or co-authored by an employee, contractor or affiliate of a national govern-
ment. As such, the Government retains a nonexclusive, royalty-free right to publish or
reproduce this article, or to allow others to do so, for Government purposes only.
DLRS ’16, September 15 2016, Boston, MA, USA
ACM ISBN 978-1-4503-4795-2/16/09. . . $15.00
DOI: http://dx.doi.org/10.1145/2988450.2988452
could rely on matrix factorization to build latent factor vec-
tors for each user. Crucially, these approaches require the
user to be identified when making recommendations. This
may not always be possible: new users to the site will not
have any profile, or users may not be logged in, or they
may have deleted their tracking information. This leads to
the problem of cold-start for recommendation methods that
require user history.
An alternative to relying on historical data is to make
session-based recommendations [23]. In this setting, the rec-
ommender system makes recommendations based only on
the behaviour of users in the current browsing session. This
avoids the aforementioned cold-start issue but we must en-
sure that the system remains accurate and responsive (i.e. the
predictions do not take too long to make). Recurrent Neu-
ral Networks (RNNs) were recently proposed in [10] for the
session-based recommendation task. The authors showed
significant improvements over traditional session-based rec-
ommendation models using an RNN. The proposed model
utilizes session-parallel mini-batch training, and also em-
ploys ranking-based loss functions for learning the model.
In this work, we further study the application of RNNs for
session-based recommendations. In particular, we examine
and adapt various techniques from the literature for this
task. These include:
• Data augmentation via sequence preprocessing and em-
bedding dropout to enhance training and reduce over-
fitting.
• Model pre-training to account for temporal shifts in
the data distribution.
• Distillation using privileged information to learn from
small datasets.
Additionally, we propose a novel alternative model that re-
duces the time and space requirements for predictions by
predicting item embeddings directly. This makes RNNs
more readily deployable in real-time settings.
Our proposed techniques were evaluated on the RecSys
Challenge 2015 data set. The effectiveness of our data aug-
mentation strategy is evidenced by relative model perfor-
mance improvements of 12.8% and 14.8% over previously re-
ported results on the Recall@20 and Mean Reciprocal Rank
@20 (MRR@20) metrics respectively. We also showed that
distillation could be successfully applied for performance
gains on small datasets. Finally, our novel item embedding
output approach significantly reduces the time and space
requirements of the RNN model.
arXiv:1606.08117v2 [cs.LG] 16 Sep 2016