He believes these themes function in modern day times, either "bringing us together through our differences or forcing us further apart".
The key concept in the theming system is the theme, or more precisely, theme function.
To alter specific theme elements in a ggplot call, we use the theme function.
The default theme function can be changed globally either in an R session with theme_set or within a ggplot call by invoking the desired theme function.
Every ggplot is controlled by a theme function that controls the general appearance of a ggplot.
To see what a complete theme function looks like in the new theming system, type theme_grey at the R prompt.
For example, theme(axis.ticks.length = unit 0.1, "in")) ggplot2 also natively supports two additional built-in theme functions: theme_bw and theme_classic.
A number of other theme functions for use in ggplot2 can be accessed from the ggthemes package authored by Jeff Arnold.
A theme function is composed of theme elements, which are individual nondata components of a graphic, such as axis.text, axis.ticks, legend.key, legend.position, and panel.background.background
Below is an example that replaces the default theme function with theme_classic: #Figure 3(b -right panel p + theme_classic + theme (legend.position=c(0.8,0.8), legend.key = element_rect(fill=NA, color=NA))+ ggtitle("pharmacokinetic Profile of Drug X") ggplot2 lets you define titles in several ways.
