In this examples of collaborative filtering we consider movie recommendation using common MovieLens data set. It represents typical cold start problem. A recommender system compares the user’s profile to reference characteristics from the user’s social environment. In the collaborative filtering approach, the recommender system identify users who share the same preference with the active user and propose items which the likeminded users favoured (and the active user has not yet seen).
We used the MovieLens 100k data set in this example. This data set consists of 100 000 ratings (15) from 943 users on 1682 movies. Each user has rated at least 20 movies. Simple demographic info for the users is included. Factorization is performed on a split data set as provided by the collector of the data. The data is split into two disjoint sets each consisting of training set and a test set with exactly 10 ratings per user.
It is common that matrices in the field of recommendation systems are very sparse (ordinary user rates only a small fraction of items from the large items’ set), therefore scipy.sparse matrix formats are used in this example.
The configuration of this example is SNMF/R factorization method using Random Vcol algorithm for initialization.
Note
MovieLens movies’ rating data set used in this example is not included in the datasets and need to be downloaded. Download links are listed in the datasets. Download compressed version of the MovieLens 100k. To run the example, the extracted data set must exist in the MovieLens directory under datasets.
Note
No additional knowledge in terms of ratings’ timestamps, information about items and their genres or demographic information about users is used in this example.
To run the example simply type:
python recommendations.py
or call the module’s function:
import nimfa.examples
nimfa.examples.recommendations.run()
Note
This example uses matplotlib library for producing visual interpretation of the RMSE error measure.
Perform SNMF/R factorization on the sparse MovieLens data matrix.
Return basis and mixture matrices of the fitted factorization model.
Parameters:  V (numpy.matrix) – The MovieLens data matrix. 

Read movies’ ratings data from MovieLens data set.
Parameters:  data_set (str) – Name of the split data set to be read. 

Compute the RMSE error rate on MovieLens data set.
Parameters: 


Run SNMF/R on the MovieLens data set.
Factorization is run on ua.base, ua.test and ub.base, ub.test data set. This is MovieLens’s data set split of the data into training and test set. Both test data sets are disjoint and with exactly 10 ratings per user in the test set.