library(ggplot2)


values1 <- c(rnorm(100, mean=50, sd=15), rnorm(100, mean=75, sd=15), rnorm(100, mean=100, sd=15))
values2 <- c(rnorm(100, mean=20, sd=10), rnorm(100, mean=30, sd=10),rnorm(100, mean=40, sd=10))
values3 <- runif(300, min = 1, max = 6)
df <- data.frame(values1, values2, values3)

#scatter plot
ggplot(df, aes(values1, values2)) +
  geom_point(aes(size=values3))

#adding transparency to the dots with alpha=
ggplot(df, aes(values1, values2)) +
  geom_point(aes(size=values3), alpha=.3)

#adding color
ggplot(df, aes(values1, values2)) +
  geom_point(aes(size=values3), color="blue", alpha=.3)

#colorscaling with viridis
ggplot(df, aes(values1, values2)) +
  geom_point(aes(size=values3, color=values3), alpha=.5) +
  scale_color_viridis_c()