ggplot2 legend : Easy steps to change the position and the appearance of a graph legend in R software


The goal of this R tutorial is to describe how to change the legend of a graph generated using ggplot2 package.

Data

ToothGrowth data is used in the examples below :

# Convert the variable dose from numeric to factor variable
ToothGrowth$dose <- as.factor(ToothGrowth$dose)
head(ToothGrowth)
##    len supp dose
## 1  4.2   VC  0.5
## 2 11.5   VC  0.5
## 3  7.3   VC  0.5
## 4  5.8   VC  0.5
## 5  6.4   VC  0.5
## 6 10.0   VC  0.5

Make sure that the variable dose is converted as a factor variable using the above R script.

Example of plot

library(ggplot2)
p <- ggplot(ToothGrowth, aes(x=dose, y=len, fill=dose)) + 
  geom_boxplot()
p

ggplot2 legend, graph, R software

Change the legend position

The position of the legend can be changed using the function theme() as follow :

p + theme(legend.position="top")
p + theme(legend.position="bottom")

ggplot2 legend, graph, R softwareggplot2 legend, graph, R software

The allowed values for the arguments legend.position are : “left”,“top”, “right”, “bottom”.

Note that, the argument legend.position can be also a numeric vector c(x,y). In this case it is possible to position the legend inside the plotting area. x and y are the coordinates of the legend box. Their values should be between 0 and 1. c(0,0) corresponds to the “bottom left” and c(1,1) corresponds to the “top right” position.

p + theme(legend.position = c(0.8, 0.2))

ggplot2 legend, graph, R software

Change the legend title and text font styles

# legend title
p + theme(legend.title = element_text(colour="blue", size=10, 
                                      face="bold"))
# legend labels
p + theme(legend.text = element_text(colour="blue", size=10, 
                                     face="bold"))

ggplot2 legend, graph, R softwareggplot2 legend, graph, R software

Change the background color of the legend box

# legend box background color
p + theme(legend.background = element_rect(fill="lightblue", 
                                  size=0.5, linetype="solid"))
p + theme(legend.background = element_rect(fill="lightblue",
                                  size=0.5, linetype="solid", 
                                  colour ="darkblue"))

ggplot2 legend, graph, R softwareggplot2 legend, graph, R software

Change the order of legend items

To change the order of items to “2”, “0.5”, “1” :

p + scale_x_discrete(limits=c("2", "0.5", "1"))

ggplot2 legend, graph, R software

Remove the plot legend

# Remove only the legend title
p + theme(legend.title = element_blank())
# Remove the plot legend
p + theme(legend.position='none')

ggplot2 legend, graph, R softwareggplot2 legend, graph, R software

Remove slashes in the legend of a bar plot

# Default plot
ggplot(data=ToothGrowth, aes(x=dose, fill=dose)) + geom_bar()
# Change bar plot border color, 
# but slashes are added in the legend
ggplot(data=ToothGrowth, aes(x=dose, fill=dose)) +
  geom_bar(colour="black")
# Hide the slashes: 
  #1. plot the bars with no border color,
  #2. plot the bars again with border color, but with a blank legend.
ggplot(data=ToothGrowth, aes(x=dose, fill=dose))+ 
  geom_bar() + 
  geom_bar(colour="black", show_guide=FALSE)

ggplot2 legend, graph, R softwareggplot2 legend, graph, R softwareggplot2 legend, graph, R software

guides() : set or remove the legend for a specific aesthetic

It’s possible to use the function guides() to set or remove the legend of a particular aesthetic(fill, color, size, shape, etc).

mtcars data sets are used :

# Prepare the data : convert cyl and gear to factor variables
mtcars$cyl<-as.factor(mtcars$cyl)
mtcars$gear <- as.factor(mtcars$gear)
head(mtcars)
##                    mpg cyl disp  hp drat    wt  qsec vs am gear carb
## Mazda RX4         21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
## Mazda RX4 Wag     21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
## Datsun 710        22.8   4  108  93 3.85 2.320 18.61  1  1    4    1
## Hornet 4 Drive    21.4   6  258 110 3.08 3.215 19.44  1  0    3    1
## Hornet Sportabout 18.7   8  360 175 3.15 3.440 17.02  0  0    3    2
## Valiant           18.1   6  225 105 2.76 3.460 20.22  1  0    3    1

Default plot without guide specification

The R code below creates a scatter plot. The color and the shape of the points are determined by the factor variables cyl and gear, respectively. The size of the points are controlled by the variable qsec.

p <- ggplot(data = mtcars, 
    aes(x=mpg, y=wt, color=cyl, size=qsec, shape=gear))+
    geom_point()
# Print the plot without guide specification
p

ggplot2 legend, graph, R software

Change the legend position for multiple guides

# Change the legend position
p +theme(legend.position="bottom")

ggplot2 legend, graph, R software

# Horizontal legend box
p +theme(legend.position="bottom", legend.box = "horizontal")

ggplot2 legend, graph, R software

Change the order for multiple guides

The function guide_legend() is used :

p+guides(color = guide_legend(order=1),
         size = guide_legend(order=2),
         shape = guide_legend(order=3))

ggplot2 legend, graph, R software

If a continuous color is used, the order of the color guide can be changed using the function guide_colourbar() :

qplot(data = mpg, x = displ, y = cty, size = hwy,
      colour = cyl, shape = drv) +
  guides(colour = guide_colourbar(order = 1),
         alpha = guide_legend(order = 2),
         size = guide_legend(order = 3))

ggplot2 legend, graph, R software

Remove a legend for a particular aesthetic

The R code below removes the legend for the aesthetics color and size :

p+guides(color = FALSE, size = FALSE)

ggplot2 legend, graph, R software

Removing a particular legend can be done also when using the functions scale_xx. In this case the argument guide is used as follow :

# Remove legend for the point shape
p+scale_shape(guide=FALSE)
# Remove legend for size
p +scale_size(guide=FALSE)
# Remove legend for color
p + scale_color_manual(values=c('#999999','#E69F00','#56B4E9'),
                       guide=FALSE)

ggplot2 legend, graph, R softwareggplot2 legend, graph, R softwareggplot2 legend, graph, R software

Infos

This analysis has been performed using R software (ver. 3.1.0) and ggplot2 (ver. 1.0.0)


Enjoyed this article? I’d be very grateful if you’d help it spread by emailing it to a friend, or sharing it on Twitter, Facebook or Linked In.

Show me some love with the like buttons below... Thank you and please don't forget to share and comment below!!
Avez vous aimé cet article? Je vous serais très reconnaissant si vous aidiez à sa diffusion en l'envoyant par courriel à un ami ou en le partageant sur Twitter, Facebook ou Linked In.

Montrez-moi un peu d'amour avec les like ci-dessous ... Merci et n'oubliez pas, s'il vous plaît, de partager et de commenter ci-dessous!






This page has been seen 201382 times