Section 13 Grammar of Graphics

• The original R graphics package is referred to as base graphics.

• Grammar of Graphics: ggplot2 by Hadley Wickham

Grammar of Graphics

In brief, the grammar tells us that a statistical graphic is a mapping from data to aesthetic attributes (colour, shape, size) of geometric objects (points, lines, bars). The plot may also contain statistical transformations of the data and is drawn on a specific coordinates system.

13.1 Essential part

Arguments	Explanation
data=	The DATA that you want to plot
geom_	The GEOMETRIC shapes that will represent the data.
aes()	AESTHETICS of the geometric and statistical objects, such as color, size, shape and position.

13.2 Advanced part

Arguments	Explanation
stat_	STATISTICAL summaries of the data that can be plotted, such as quantiles, fitted curves (loess, linear models, etc.), sums and so o.
scale_	MAP between the data and the aesthetic dimensions, such as data range to plot width or factor values to colors
coord_	The transformation used for mapping data COORDINATES into the plane of the data rectangle.
facet_	The arrangement of the data into a grid of plots
theme	The overall visual THEMES of a plot: background, grids, axe, default typeface, sizes, colors, etc.

• The data is what we want to visualize. It consists of variables, which are stored as columns in a data.frame.

• The geom is the geometric objects that are drawn to represent the data, such as bars, lines, and points - what the data would look like. For many geom options, there is equivalent stat options. For example, geom_boxplot and stat_boxplot.

• The aes is aesthetic attribute, or aesthetics, are visual properties of geoms, such as x and y position, line color, point shapes, etc. The aesthetic mapping maps the data values to aesthetics - how the data be presented.