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In R, circles can be drawn on a plot by using the function ‘symbols’ and specifying the type of symbol as ‘circle’. This can be done by supplying the x and y coordinates of the center of the circle along with the radius of the circle, as well as any other desired graphical parameters such as colour and size. The ‘plot’ function can then be used to draw the circle on the plot.
You can use the following methods to draw a circle in a plot in R:
Method 1: Draw Circle Using Base R
library(plotrix)
#create scatter plot
plot(x, y)
#add circle at specific (x, y) coordinates with specific radius
draw.circle(x=3, y=8, radius=.5)
Method 2: Draw Circle Using ggplot2
library(ggplot2) library(ggforce) #create scatter plot with circle at specific location with specific radius ggplot(data = df, aes(x, y)) + geom_point() + geom_circle(aes(x0=3, y0=8, r=1), inherit.aes=FALSE) + coord_fixed()
The following examples shows how to use each method in practice.
Example 1: Draw Circle Using Base R
To draw a circle on a plot in base R, you need to first install and load the plotrix package:
install.packages('plotrix')
library(plotrix)
Next, we can use the draw.circle() function from the plotrix package to add a circle to a scatter plot in base R:
#create data frame
df <- data.frame(x=c(1, 2, 2, 3, 3, 4, 8),
y=c(2, 4, 5, 4, 7, 9, 10))
#create scatter plot
plot(df$x, df$y)
#add circle
draw.circle(x=3, y=8, radius=.5)
You can also use the draw.circle() function multiple times to plot multiple circles on the same plot:
#create data frame
df <- data.frame(x=c(1, 2, 2, 3, 3, 4, 8),
y=c(2, 4, 5, 4, 7, 9, 10))
#create scatter plot
plot(df$x, df$y)
#add multiple circles to plot
draw.circle(x=3, y=8, radius=.5)
draw.circle(x=4, y=5, radius=.5, border='red', col='lightblue', lwd=5, lty='dashed')
Notice that multiple circles have been added to the plot at the (x, y) coordinates that we specified.
Example 2: Draw Circle Using ggplot2
install.packages('ggplot2')
install.packages('ggforce')
library(ggplot2)
library(ggforce)
Next, we can use the geom_circle() function from the ggforce package to add a circle to a scatter plot in ggplot2:
#create data frame
df <- data.frame(x=c(1, 2, 2, 3, 3, 4, 8),
y=c(2, 4, 5, 4, 7, 9, 10))
#create scatter plot with circle
ggplot(data = df, aes(x, y)) +
geom_point() +
geom_circle(aes(x0=3, y0=8, r=1), linetype='dashed', color='red',
fill='lightblue', lwd=1.5, inherit.aes=FALSE) +
coord_fixed()
The circle is placed in the exact (x, y) coordinates that we specified.
Note: If you don’t use the coord_fixed() argument, the circle may appear as an ellipse instead.
The following tutorials explain how to perform other common tasks in R: