How to Create a Bubble Chart in R using GGPlot2

Prerequisites

• Load the ggplot2 package and set the theme function theme_bw() as the default theme:

library(ggplot2)
theme_set(
  theme_bw() + 
    theme(legend.position = "top")
  )

• Data preparation

Demo dataset: mtcars. The variable cyl is used as grouping variable.

# Load data
data("mtcars")
df <- mtcars

# Convert cyl as a grouping variable
df$cyl <- as.factor(df$cyl)

# Inspect the data
head(df[, c("wt", "mpg", "cyl", "qsec")], 4)

##                  wt  mpg cyl qsec
## Mazda RX4      2.62 21.0   6 16.5
## Mazda RX4 Wag  2.88 21.0   6 17.0
## Datsun 710     2.32 22.8   4 18.6
## Hornet 4 Drive 3.21 21.4   6 19.4

Create a bubble chart

In a bubble chart, points size is controlled by a continuous variable, here qsec. In the R code below, the argument alpha is used to control color transparency. alpha should be between 0 and 1.

ggplot(df, aes(x = wt, y = mpg)) + 
  geom_point(aes(color = cyl, size = qsec), alpha = 0.5) +
  scale_color_manual(values = c("#00AFBB", "#E7B800", "#FC4E07")) +
  scale_size(range = c(0.5, 12))  # Adjust the range of points size