Version 0.9.0 of the ggplot2 package contains a number of
changes that provide a user with more
flexibility and greater ease of use in the construction of a
ggplot. The two most evident improvements from a user's
perspective are: (i) the help
pages have been expanded considerably, with many new examples; and
(ii) the computing time has been reduced significantly. Several new
geoms are introduced, as well as a few new stat_
functions. These will be described in the sections to follow.
Control over legends is greatly expanded in version 0.9.0. Two functions are
discussed in this section: guide_legend and
guide_colorbar. We discuss these first because they will be
used extensively in the sections to follow.
In the grammar of graphics, there are two types of guides: scale
guides and annotation guides. In the former group lie positional guides
and legends. Annotation guides include geom_text, annotate
and the new annotation functions.
Each guide function has a number of arguments. The following table lists those that are common to both legend guides and colorbar guides:
Category Argument Notes
title title legend title
title.position left, right, top, bottom
title.theme uses theme_text
title.hjust horizontal justification
title.vjust vertical justification
label label TRUE means labels are drawn
label.position left, right, top, bottom
label.theme uses theme_text
label.hjust horizontal justification
label.vjust vertical justification
key options default.unit measurement unit
direction horizontal or vertical
reverse reverse direction of keys
This function provides a user with several options to control features of a legend guide, including titles, labels, the height and width of legend keys, the direction of the legend and several other options that are useful when a large number of categories exist.
The code below creates four rows of legend keys, increases the
font size of the legend title and emboldens it:
The following example concerns an application that comes up occasionally
on the ggplot2 list: overriding the alpha transparency value in
the legend so that the values of an aesthetic are visible in the legend key.
The relevant argument is override.aes: in the left side plot, the
very low alpha value makes it impossible to see the legend key items, but
override.aes resets the alpha value in the legend to make them
visible in the right hand plot.
