Getting Started with Python Data Analysis

Computer science: We need this knowledge to provide abstractions for efficient data processing. Basic Python programming experience is required to follow the next chapters. We will introduce Python libraries used in data analysis.

Artificial intelligence and machine learning: If computer science knowledge helps us to program data analysis tools, artificial intelligence and machine learning help us to model the data and learn from it in order to build smart products.

Statistics and mathematics: We cannot extract useful information from raw data if we do not use statistical techniques or mathematical functions.

Knowledge domain: Besides technology and general techniques, it is important to have an insight into the specific domain. What do the data fields mean? What data do we need to collect? Based on the expertise, we explore and analyze raw data by applying the above techniques, step by step.

Data requirements: We have to define what kind of data will be collected based on the requirements or problem analysis. For example, if we want to detect a user's behavior while reading news on the internet, we should be aware of visited article links, dates and times, article categories, and the time the user spends on different pages.

Data collection: Data can be collected from a variety of sources: mobile, personal computer, camera, or recording devices. It may also be obtained in different ways: communication, events, and interactions between person and person, person and device, or device and device. Data appears whenever and wherever in the world. The problem is how we can find and gather it to solve our problem? This is the mission of this step.

Data processing: Data that is initially obtained must be processed or organized for analysis. This process is performance-sensitive. How fast can we create, insert, update, or query data? When building a real product that has to process big data, we should consider this step carefully. What kind of database should we use to store data? What kind of data structure, such as analysis, statistics, or visualization, is suitable for our purposes?

Data cleaning: After being processed and organized, the data may still contain duplicates or errors. Therefore, we need a cleaning step to reduce those situations and increase the quality of the results in the following steps. Common tasks include record matching, deduplication, and column segmentation. Depending on the type of data, we can apply several types of data cleaning. For example, a user's history of visits to a news website might contain a lot of duplicate rows, because the user might have refreshed certain pages many times. For our specific issue, these rows might not carry any meaning when we explore the user's behavior so we should remove them before saving it to our database. Another situation we may encounter is click fraud on news—someone just wants to improve their website ranking or sabotage a website. In this case, the data will not help us to explore a user's behavior. We can use thresholds to check whether a visit page event comes from a real person or from malicious software.

Exploratory data analysis: Now, we can start to analyze data through a variety of techniques referred to as exploratory data analysis. We may detect additional problems in data cleaning or discover requests for further data. Therefore, these steps may be iterative and repeated throughout the whole data analysis process. Data visualization techniques are also used to examine the data in graphs or charts. Visualization often facilitates understanding of data sets, especially if they are large or high-dimensional.

Modelling and algorithms: A lot of mathematical formulas and algorithms may be applied to detect or predict useful knowledge from the raw data. For example, we can use similarity measures to cluster users who have exhibited similar news-reading behavior and recommend articles of interest to them next time. Alternatively, we can detect users' genders based on their news reading behavior by applying classification models such as the Support Vector Machine (SVM) or linear regression. Depending on the problem, we may use different algorithms to get an acceptable result. It can take a lot of time to evaluate the accuracy of the algorithms and choose the best one to implement for a certain product.

Data product: The goal of this step is to build data products that receive data input and generate output according to the problem requirements. We will apply computer science knowledge to implement our selected algorithms as well as manage the data storage.

Weka: This is the library that I became familiar with the first time I learned about data analysis. It has a graphical user interface that allows you to run experiments on a small dataset. This is great if you want to get a feel for what is possible in the data processing space. However, if you build a complex product, I think it is not the best choice, because of its performance, sketchy API design, non-optimal algorithms, and little documentation (http://www.cs.waikato.ac.nz/ml/weka/).

Mallet: This is another Java library that is used for statistical natural language processing, document classification, clustering, topic modeling, information extraction, and other machine-learning applications on text. There is an add-on package for Mallet, called GRMM, that contains support for inference in general, graphical models, and training of Conditional random fields (CRF) with arbitrary graphical structures. In my experience, the library performance and the algorithms are better than Weka. However, its only focus is on text-processing problems. The reference page is at http://mallet.cs.umass.edu/.

Mahout: This is Apache's machine-learning framework built on top of Hadoop; its goal is to build a scalable machine-learning library. It looks promising, but comes with all the baggage and overheads of Hadoop. The homepage is at http://mahout.apache.org/.

Spark: This is a relatively new Apache project, supposedly up to a hundred times faster than Hadoop. It is also a scalable library that consists of common machine-learning algorithms and utilities. Development can be done in Python as well as in any JVM language. The reference page is at https://spark.apache.org/docs/1.5.0/mllib-guide.html.

Vowpal Wabbit: This library is a fast, out-of-core learning system sponsored by Microsoft Research and, previously, Yahoo! Research. It has been used to learn a tera-feature (1012) dataset on 1,000 nodes in one hour. More information can be found in the publication at http://arxiv.org/abs/1110.4198.

MultiBoost: This package is a multiclass, multi label, and multitask classification boosting software implemented in C++. If you use this software, you should refer to the paper published in 2012 in the JournalMachine Learning Research, MultiBoost: A Multi-purpose Boosting Package, D.Benbouzid, R. Busa-Fekete, N. Casagrande, F.-D. Collin, and B. Kégl.

MLpack: This is also a C++ machine-learning library, developed by the Fundamental Algorithmic and Statistical Tools Laboratory (FASTLab) at Georgia Tech. It focusses on scalability, speed, and ease-of-use, and was presented at the BigLearning workshop of NIPS 2011. Its homepage is at http://www.mlpack.org/about.html.

Caffe: The last C++ library we want to mention is Caffe. This is a deep learning framework made with expression, speed, and modularity in mind. It is developed by the Berkeley Vision and Learning Center (BVLC) and community contributors. You can find more information about it at http://caffe.berkeleyvision.org/.

Statsmodels: This is a great Python library for statistical modeling and is mainly used for predictive and exploratory analysis.

Modular toolkit for data processing (MDP): This is a collection of supervised and unsupervised learning algorithms and other data processing units that can be combined into data processing sequences and more complex feed-forward network architectures (http://mdp-toolkit.sourceforge.net/index.html).

Orange: This is an open source data visualization and analysis for novices and experts. It is packed with features for data analysis and has add-ons for bioinformatics and text mining. It contains an implementation of self-organizing maps, which sets it apart from the other projects as well (http://orange.biolab.si/).

Mirador: This is a tool for the visual exploration of complex datasets, supporting Mac and Windows. It enables users to discover correlation patterns and derive new hypotheses from data (http://orange.biolab.si/).

RapidMiner: This is another GUI-based tool for data mining, machine learning, and predictive analysis (https://rapidminer.com/).

Theano: This bridges the gap between Python and lower-level languages. Theano gives very significant performance gains, particularly for large matrix operations, and is, therefore, a good choice for deep learning models. However, it is not easy to debug because of the additional compilation layer.

Natural language processing toolkit (NLTK): This is written in Python with very unique and salient features.