ggplot2 texts : Add text annotations to a graph in R software

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To add a text to a plot generated using ggplot2, the functions below can be used :

  • geom_text()
  • annotate()
  • annotation_custom()

Create some data

df <- data.frame(x=1:3, y=1:3, 
               name=c("Text1", "Text with \n 2 lines", "Text3"))
head(df)
##   x y                 name
## 1 1 1                Text1
## 2 2 2 Text with \n 2 lines
## 3 3 3                Text3

Text annotations using the function geom_text

library(ggplot2)
# Simple scatter plot
sp <- ggplot(data = df, aes(x, y, label=name)) +
  geom_point()+xlim(0,3.5)+ylim(0,3.5)
# Add texts
sp + geom_text()
# Change the size of the texts
sp + geom_text(size=6)
# Change vertical and horizontal adjustement
sp +  geom_text(hjust=0, vjust=0)
# Change fontface. Allowed values : 1(normal),
# 2(bold), 3(italic), 4(bold.italic)
sp + geom_text(aes(fontface=2))

ggplot2 add texts to a graph in Rggplot2 add texts to a graph in Rggplot2 add texts to a graph in Rggplot2 add texts to a graph in R

Change the text color and size by groups

It’s possible to change the appearance of the texts using aesthetics (color, size,…) :

sp2 <- ggplot(mtcars, aes(x=wt, y=mpg, label=rownames(mtcars)))+
  geom_point()
# Color by groups
sp2 + geom_text(aes(color=factor(cyl)))

ggplot2 add texts to a graph in R

# Set the size of the text using a continuous variable
sp2 + geom_text(aes(size=wt))

ggplot2 add texts to a graph in R

sp2 + geom_text(aes(size=wt)) + scale_size(range=c(3,6))

ggplot2 add texts to a graph in R

Add a text annotation at a particular coordinate

The functions geom_text() and annotate() can be used :

# Solution 1
sp2 + geom_text(x=3, y=30, label="Scatter plot")
# Solution 2
sp2 + annotate(geom="text", x=3, y=30, label="Scatter plot",
              color="red")

ggplot2 add texts to a graph in Rggplot2 add texts to a graph in R

annotation_custom : Add a static text annotation in the top-right, top-left, …

The functions annotation_custom() and textGrob() are used to add static annotations which are the same in every panel.The grid package is required :

library(grid)
# Create a text
grob <- grobTree(textGrob("Scatter plot", x=0.1,  y=0.95, hjust=0,
  gp=gpar(col="red", fontsize=13, fontface="italic")))
# Plot
sp2 + annotation_custom(grob)

ggplot2 add texts to a graph in R

Facet : In the plot below, the annotation is at the same place (in each facet) even if the axis scales vary.

sp2 + annotation_custom(grob)+facet_wrap(~cyl, scales="free")

ggplot2 add texts to a graph in R

Infos

This analysis has been performed using R software (ver. 3.1.2) and ggplot2 (ver. )


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