cowplot (version 0.5.0)

add_sub: Add annotation underneath a plot

Description

This function can add an arbitrary label or mathematical expression underneath the plot, similar to the sub parameter in base R.

Usage

add_sub(plot, label, x = 0.5, y = 0.5, hjust = 0.5, vjust = 0.5,
  vpadding = grid::unit(1, "lines"), fontfamily = "", fontface = "plain",
  colour = "black", size = 14, angle = 0, lineheight = 0.9)

Arguments

plot

A ggplot object or gtable object derived from a ggplot object.

label

The label with which the plot should be annotated. Can be a plotmath expression.

x

The x position of the label

y

The y position of the label

hjust

Horizontal justification

vjust

Vertical justification

vpadding

Vertical padding. The total vertical space added to the label, given in grid units. By default, this is added equally above and below the label. However, by changing the y and vjust parameters, this can be changed.

fontfamily

The font family

fontface

The font face ("plain", "bold", etc.)

colour

Text color

size

Point size of text

angle

Angle at which text is drawn

lineheight

Line height of text

Value

• A gtable object holding the modified plot.

Details

The exact location where the label is placed is controlled by the parameters x, y, hjust, and vjust. By default, all these parameters are set to 0.5, which places the label centered underneath the plot panel. A value of x = 0 indicates the left boundary of the plot panel and a value of x = 1 indicates the right boundary. The parameter hjust works just as elsewhere in ggplot2. Thus, x = 0, hjust = 0 places the label left-justified at the left boundary of the plot panel, x = 0.5, hjust = 0.5 places the label centered underneath the plot panel, and x = 1, hjust = 1 places it right-justified at the right boundary of the plot panel. x-values below 0 or above 1 are allowed, and they move the label beyond the limits of the plot panel.

The y coordinates are relative to the added vertical space that is introduced underneath the x-axis label to place the annotation. A value of y=0 indicates the bottom-most edge of that space and a value of y=1 indicates the top-most edge of that space. The total height of the added space is given by the height needed to draw the label plus the value of vpadding. Thus, if y=0, vjust=0 then the extra padding is added entirely above the label, if y=1, vjust=1 then the extra padding is added entirely below the label, and if y=0.5, vjust=0.5 (the default) then the extra padding is added equally above and below the label. As is the case with x, y-values outside the range 0-1 are allowed. In particular, for sufficiently large values of y, the label will eventually be located inside the plot panel.

Examples

p1 <- ggplot(mtcars, aes(mpg, disp)) + geom_line(colour = "blue") + background_grid(minor='none')
ggdraw(add_sub(p1, "This is an annotation.\nAnnotations can span multiple lines."))

# You can also do this repeatedly. Just be aware that new annotations are added above previous ones:
p2 <- add_sub(p1, expression(paste(a^2+b^2, "= ", c^2)))
p3 <- add_sub(p2, "This formula has no relevance here:", y  = 0, vjust = 0)
ggdraw(p3)

#This code also works with faceted plots:
plot.iris <- ggplot(iris, aes(Sepal.Length, Sepal.Width)) +
  geom_point() + facet_grid(. ~ Species) + stat_smooth(method = "lm") +
  background_grid(major = 'y', minor = "none") + # add thin horizontal lines
  panel_border() # and a border around each panel
p2 <- add_sub(plot.iris, "Annotation underneath a faceted plot, left justified.", x = 0, hjust = 0)
ggdraw(p2)

# Finally, it is possible to move the annotation inside of the plot if desired.
ggdraw(add_sub(p1, "Annotation inside plot", vpadding=grid::unit(0, "lines"),
       y = 6, x = 0.03, hjust = 0))