it-ebooks - R for Data Science

Data science is a huge field, and theres no way you can master it by reading a single book. The goal of this book is to give you a solid foundation in the most important tools. Our model of the tools needed in a typical data science project looks something like this:

First you must import your data into R. This typically means that you take data stored in a file, database, or web API, and load it into a data frame in R. If you cant get your data into R, you cant do data science on it!

Once youve imported your data, it is a good idea to tidy it. Tidying your data means storing it in a consistent form that matches the semantics of the dataset with the way it is stored. In brief, when your data is tidy, each column is a variable, and each row is an observation. Tidy data is important because the consistent structure lets you focus your struggle on questions about the data, not fighting to get the data into the right form for different functions.

Once you have tidy data, a common first step is to transform it. Transformation includes narrowing in on observations of interest (like all people in one city, or all data from the last year), creating new variables that are functions of existing variables (like computing velocity from speed and time), and calculating a set of summary statistics (like counts or means). Together, tidying and transforming are called wrangling, because getting your data in a form thats natural to work with often feels like a fight!

Once you have tidy data with the variables you need, there are two main engines of knowledge generation: visualisation and modelling. These have complementary strengths and weaknesses so any real analysis will iterate between them many times.

Visualisation is a fundamentally human activity. A good visualisation will show you things that you did not expect, or raise new questions about the data. A good visualisation might also hint that youre asking the wrong question, or you need to collect different data. Visualisations can surprise you, but dont scale particularly well because they require a human to interpret them.

Models are complementary tools to visualisation. Once you have made your questions sufficiently precise, you can use a model to answer them. Models are a fundamentally mathematical or computational tool, so they generally scale well. Even when they dont, its usually cheaper to buy more computers than it is to buy more brains! But every model makes assumptions, and by its very nature a model cannot question its own assumptions. That means a model cannot fundamentally surprise you.

The last step of data science is communication, an absolutely critical part of any data analysis project. It doesnt matter how well your models and visualisation have led you to understand the data unless you can also communicate your results to others.

Surrounding all these tools is programming. Programming is a cross-cutting tool that you use in every part of the project. You dont need to be an expert programmer to be a data scientist, but learning more about programming pays off because becoming a better programmer allows you to automate common tasks, and solve new problems with greater ease.

Youll use these tools in every data science project, but for most projects theyre not enough. Theres a rough 80-20 rule at play; you can tackle about 80% of every project using the tools that youll learn in this book, but youll need other tools to tackle the remaining 20%. Throughout this book well point you to resources where you can learn more.