  Most of the existing recommender systems are based only on the rating data,
and they ignore other sources of information that might increase the quality of
recommendations, such as textual reviews, or user and item characteristics.
Moreover, the majority of those systems are applicable only on small datasets
(with thousands of observations) and are unable to handle large datasets (with
millions of observations). We propose a recommender algorithm that combines a
rating modelling technique (i.e., Latent Factor Model) with a topic modelling
method based on textual reviews (i.e., Latent Dirichlet Allocation), and we
extend the algorithm such that it allows adding extra user- and item-specific
information to the system. We evaluate the performance of the algorithm using
Amazon.com datasets with different sizes, corresponding to 23 product
categories. After comparing the built model to four other models we found that
combining textual reviews with ratings leads to better recommendations.
Moreover, we found that adding extra user and item features to the model
increases its prediction accuracy, which is especially true for medium and
large datasets.
