The Grammar of Graphics
Every time you draw a chart, you are actually doing many different things. You are:
Defining the data that will be shown to the user
Determining how to summarize or transform the data
Determining the graphical objects that will be used to represent the data
Determining how to divide the data, and how to show different partitions
Determining how the chart looks
When you draw a chart with most conventional tools (such as spreadsheets and presentation programs), you begin by picking a style of chart like a scatter plot, a pie chart, or a bar chart for your data. You may then refine the chart slightly by tweaking the size, color, and other visual parameters. These tools don’t reflect the thought process in drawing a chart. If you have to summarize your data before plotting (for example, when plotting a histogram), it can be awkward to do so. It is often hard to tweak how the results are displayed. Worst of all, it can be difficult to pick a different object to represent the data.
The grammar of graphics is designed to help separate each step of
the charting process. This can help you decide the best way to visualize
data, and is especially helpful for defining new types of plots. Each of
these different aspects of the charting process is given a name in
ggplot2
; the tool reflects the
language. The ggplot2
package includes
a variety of functions for altering each component of a plot. (The
qplot
function above simplifies this process by allowing you to use arguments to ...
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