Non-Personalized Recommender systems with Pandas and Python

Hi all,

At the last PythonBrasil I gave a tutorial about Python and Data Analysis focused on recommender systems, the main topic I've been studying for the last years. There is a popular python package among the statisticians and data scientists called Pandas. I watched several talks and keynotes about it, but I didn't have a try on it. The tutorial gave me this chance and after the tutorial me and the audience fell quite excited about the potential and power that this library gives.

This post starts a series of articles that I will write about recommender systems and even the introduction for the new-old refreshed library that I am working on:  Crab,  a python library for building recommender systems. :)

This post starts with the first topic about the theme: Non-personalized Recommender Systems and giving several examples with the python package Pandas.  In future I will also post an alternative version of this post but referencing Crab, about how it works with him.

But first let's introduce what Pandas is.

Introduction to Pandas

Pandas is a data analysis library for Python that is great for data preparation, joining and ultimately generating well-formed, tabular data that's easy to use in a variety of visualization tools or (as we will see here) machine learning applications. For further introduction about pandas, check this website or this notebook.

Non-personalized Recommenders

Non-personalized recommenders can  recommend items to consumers based on what other consumers have said about the items on average. That is, the recommendations are independent of the customer,  so each customer gets the same recommendation.  For example, if you go to amazon.com as an anonymous user it shows items that are currently viewed by other members.

Generally the recommendations come in two flavours: predictions or recommendations. In case of predictions are simple statements that are formed in form of scores, stars or counts.  On the other hand, recommendations are generally simple a list of items shown without any number associated with it.

Let's going by an example:

Simple Prediction using Average

The score in the scale of 1 to 5 to the book Programming Collective Intelligence was 4.5 stars out of 5.
This is an example of a simple prediction. It displays a simple average of other customer reviews about the book.
The math behind it is quite simple:

Score = ( 65 * 5 + 18 * 4 + 7 * 3 +  4 * 2 +  2 * 1)
Score =  428/ 96
Score = 4.45 ˜= 4.5 out of 5 stars

In the same page it also displays the information about the other books which the customers bought after buying Programming Collective Intelligence. A list of recommended books presented to anyone who visits the product's page. It is an example of recommendation.

But how Amazon came up with those recommendations ? There are several techniques that could be applied to provide those recommendations. One would be the association rules mining, a data mining technique to generate a set of  rules and combinatios of items that were bought together. Or it could be a simple average measure based on the proportion of who bought x and y by who bought x. Let's explain using some maths:

Let X be the number of customers who purchased the book Programming Collective Intelligence. Let Y be the other books they purchased. You need to compute the ration given below for each book and sort them by descending order.  Finally, pick up the top K books and show them as related. :D

Score(X, Y) =  Total Customers who purchased X and Y / Total Customers who purchased X

Using this simple score function for all the books you wil achieve:


Python for Data Analysis                                                 100%

Startup Playbook                                                              100%

MongoDB Definitive Guid                                                0 %

Machine Learning for Hackers                                          0%

As we imagined the book  Python for Data Analysis makes perfect sense. But why did the book  Startup Playbook came to the top when it has been purchased by customers who have not purchased Programming Collective Intelligence.  This a famous trick in e-commerce applications called banana trap.   Let's explain: In a grocery store most of customers will buy bananas. If someones buys a razor and a banana then you cannot tell that the purchase of a razor influenced the purchase of banana.  Hence we need to adjust the math to handle this case as well. Modfying the version:

Score(X, Y) =  (Total Customers who purchased X and Y / Total Customers who purchased X) / 

         (Total Customers who did not purchase X but got Y / Total Customers who did not purchase X)

Substituting the number we get:

Python for Data Analysis =   ( 2 / 2 ) /  ( 1 / 3) =  1 / 1/3  =  3 

Startup Playbook   =   ( 2 / 2)  /  ( 3 /  3)  =  1 

The denominator acts as a normalizer and you can see that Python for Data Analysis clearly stands out.  Interesting, doesn't ? 

The next article I will work more with non-personalized recommenders, presenting some ranking algorithms that I developed for Atepassar.com for ranking  professors. :)

Examples with real dataset (let's play with CourseTalk dataset)

To present non-personalized recommenders let's play with some data. I decided to crawl the data from the popular ranking site for MOOC's  Course Talk.  It is an aggregator of several MOOC's where people can rate the courses and write reviews.  The dataset is a mirror from the date  10/11/2013 and it is only used here for study purposes.

Let's use Pandas to read all the data and start showing what we can do with Python and present a list of top courses ranked by some non-personalized metrics :)

Update: For better analysis I hosted all the code provided at the IPython Notebook at the following link by using nbviewer.

All the dataset and source code will be provided at crab's github, the idea is to work on those notebooks to provide a future book about recommender systems :)

I hope you enjoyed this article,  and stay tunned for the next one about another type of non-personalized recommenders:  Ranking algorithms for vote up/vote down systems!

Special thanks for the tutorial of Diego Manillof :)

Cheers,

Marcel Caraciolo

Ruby in the world of Recommendations (also machine learning, statistics and visualizations)

Hello everyone!

I am back with lots of news and articles! I've been quite busy but I returned. In this post I'd like to share my last presentation that I gave at Frevo On'Rails Pernambuco Ruby Meeting at Recife, PE. My  Ruby developer colleagues around Recife invited me to give a lecture there.  I was quite excited about the invitation and instanlty I accepted.

I decided to research more about scientific computing with Ruby and recommender libraries written focused on Ruby either.  Unfortunately the escossistem for scientific environment in Ruby is still at very beginning.  I found several libraries but most of them were abandoned by their developers or commiters.  But I didn't give up and decided to refine my searches. I found a espectular and promising work on scientific computing with ruby called SciRuby. The goal is to por several matrix and vector representations with Ruby using C and C++ at backend. It remembered me a lot the beginnings of the library Numpy and Scipy :)

About the recommenders, I didn't find any deep work as Mahout, but I found a library called Recommendable that uses memory-based collaborative filtering.  I really liked the design of the library and the workaround of the developer on making the linear algebra operations with Redis instead of Ruby :D

All those considerations and more insights I put on my slides, feel free to share :)

Recommender Systems with Ruby (adding machine learning, statistics, etc) from Marcel Caraciolo

I hope you enjoyed, and even I love Python, I really like programming another languages :)

Regards,

Marcel

Slides and Video from my talk about Big Data with Python in Portuguese

Hi all,

It has been a while since my last technical posts. But it's for a great cause! I am writing the current book about recommender systems and it is taking some dedicated time to work on it! But great posts are coming to the blog.

I'd like to publish an on-line talk that I gave in June' 18 at #MutiraoPython, a great initiative that I started with my startup PyCursos, an learning school for teaching Python and applications on-line. It's like a Coursera MOOC's for Programming in portuguese!  This talk was part of a series of keynotes that are happening every week on-line for free using the Hangout on Air!

I gave a lecture for about two hours about Big Data with Python and presentend some tools used for data analysis. I know that I missed to explore more Pandas, Ipython, Scikit-learn. However, I decided to explore the Hadoop Architecture and MapReduce Paradigm and some code examples with Python.

It's in portuguese! But all the content is available for free! I hope you enjoy!

Video and code

Slides

Big Data com Python from Marcel Caraciolo

Review about the book Learning IPython for Interactive Computing and Data Visualization

Hi all,

I was invited to review a copy of the book recently released titled "Learning IPython for Interactive Computing and Data Visualization" by the author Cyrille Rossant.  The book focus on one of the best tools for working with Python with the interactive incremented shell IPython.  By the way, it was the time to the tool receive a special book about it.

Learning IPython for Interactive Computing and Data Visualization

IPython is covered through the six chapters using several basic examples related to scientific computing  along with another Python tools such as Matplotlib, Numpy, Pandas, etc.  The first chapters explore the IPython basics such as installation, basic commands to get used with the tool.

The next chapters introduces NumPy and Pandas basics with the IPython shell active. Don't expect advanced examples with those tools. The idea is a simple demonstration of what we can do at IPython.

There is a chapter to discuss the visualization data with graphs, plottings with IPython Notebook. However I missed more details abot IPython notebook. It lacks more deep examples related to the topic.  

I really liked the chapter 5 when they showed some basics of MPI (Message Passing Theme), although the topic wasn't vasted explored. But the introduction gives a greate potential of usefulness to the more advanced books about IPython.

The last chapter shows how to create pluggins to IPython, for instance, create an simple extension that introduces a new cell magic (write C++ code directly in the cell, and it will be automatically compiled and executed).

My conclusion about the book is that it achieves the expected goal: a technical introduction to IPython. If you want a book to explore scientific computing or a advanced stuff to IPython, this is not the the book yet. I can say that this book is a first start for much more topics about the use of IPython.  MPI, IPython notebook, etc.  I recommend the book for start exploring the IPython as reference! :D

Regards,

Marcel

Review of the book Learning Scipy for Numerical and Scientific Computing

Hi all,

I've finished reading the book "Learning Scipy for Numerical and Scientific Computing".  This book comes to the scientific python series that PacktPub are bringing to the Python Developers! Congratulations!  As the title informs: it includes Scipy, Numpy and Matplotlib.  I only missed some further information about IPython, but it wasn't the goal of the book, so it goes well even leaved out.

It covers several important topics that are not as commonly covered, specially with several snippets illustrating special functions presented at Scipy library. For the developers it will be another great reference book to complement the native docs that comes with the library.  I enjoyed the author focused more on numerical analysis functions, it is one of the most used functions at the library.  

The bool also brings chapters on more specific applications: signal processing, data mining and computational geometry.  There is an extra chapter about the integration with another languages, but I found it not dense enough to explain those integrations. I really missed more start-off examples showing how to install the f2py or how to use Scipy with C/C++. 

Overall the Learning Scipy for Numerical and Scientific Computing book is a good book on Scipy covering  lots of mathematics with examples in Python. The book has a good size and it helps the scientists and scientific developers (by the way the non-developers will face some difficulties due to the heavy math that comes with the examples) to have a good overview on the library before exploring the reference material.

Thanks Kenny for the invitation to review this book, and congratulations to Francisco for bringing one more technical book for scientific python computing to the series!

Regards,

Marcel Caraciolo