Visualizing Data

Chapter 4. Time Series

The time series is a ubiquitous type of data set. It describes how some measurable feature (for instance, population, snowfall, or items sold) has changed over a period of time. Edward Tufte credits Johann Heinrich Lambert with the formal introduction of the time series to scientific literature in the 1700s.^[2]

Because of its ubiquity, the time series is a good place to start when learning about visualization. With it we can cover:

• Acquiring a table of data from a text file

• Parsing the contents of the file into a usable data structure

• Calculating the boundaries of the data to facilitate representation

• Finding a suitable representation and considering alternatives

• Refining the representation with consideration for placement, type, line weight, and color

• Providing a means of interacting with the data so that we can compare variables against one another or against the average of the whole data set

For a straightforward data set, let’s turn to the U.S. Department of Agriculture (USDA) for statistics on beverage consumption. Government sites are a terrific resource for data; see Chapter 9 for more information about them and other sources of data.

Most methods will be implemented “by hand” in this section. Further down the line, we’ll make generalized code to handle different scenarios, such as reading a table from a file or placing labels and grid lines on a plot.

Milk, Tea, and Coffee (Acquire and Parse)

The data set we use was originally downloaded from http://www.ers.usda.gov/data/foodconsumption/foodavailqueriable.aspx ...