Default legend with ggplot2

# Load ggplot2
library(ggplot2)

# Very basic chart
basic <- ggplot(mtcars, aes(wt, mpg, colour = factor(cyl), shape = factor(vs) )) +
       geom_point()
basic

Change legend title with labs()

basic+
  labs(
         colour = "name1",
         shape = "name2"
        )

Get rid of the legend: guides() and theme()

It is possible to remove a specific part or the whole legend thanks to the theme() and the guides() function. See code below:

# Left -> get rid of one part of the legend
basic + guides(shape=FALSE)

# Right -> only the x axis is modified
basic + theme(legend.position = "none")

Control legend position with legend.position

You can place the legend literally anywhere.

To put it around the chart, use the legend.position option and specify top, right, bottom, or left. To put it inside the plot area, specify a vector of length 2, both values going between 0 and 1 and giving the x and y coordinates.

Note: the command legend.justification sets the corner that the position refers to.

# Left -> legend around the plot
basic + theme(legend.position = "bottom")

# Right -> inside the plot area
basic + theme(
    legend.position = c(.95, .95),
    legend.justification = c("right", "top"),
    legend.box.just = "right",
    legend.margin = margin(6, 6, 6, 6)
    )

Legend appearance

Here are 4 examples showing how to customize the legend main features:

• box with legend.box.: it is a rectangle that frames the legend. Give features with element_rect()
• key with legend.key: the key is the part showing the symbols. Note that symbols will automatically be the ones used on the chart
• text with legend.text: here you can control the color, the size of the right part of the legend
• title with legend.title.

# custom box around legend
basic + theme(
    legend.box.background = element_rect(color="red", size=2),
    legend.box.margin = margin(116, 6, 6, 6)
)

# custom the key
basic + theme(legend.key = element_rect(fill = "white", colour = "black"))

# custom the text
basic + theme(legend.text = element_text(size = 8, colour = "red"))

# custom the title
basic + theme(legend.title = element_text(face = "bold"))