Say I like to increase the size of only those data points where the factor variable cyl == 6. How can I do that?

ggplot(mtcars, aes(x = qsec , y = mpg, col = as.factor(cyl ))) +
  geom_point(size= 2)

I do not want to use the size option here:

ggplot(mtcars, aes(x = qsec , y = mpg, col = as.factor(cyl), size = as.factor(cyl))) +
  geom_point()

because it uses size for all factor levels.

>Solution :

Another way is to use ifelse to assign size.

library(ggplot2)

ggplot(mtcars, aes(x = qsec , y = mpg, col = as.factor(cyl), size = ifelse(cyl == 6, 4, 3))) +
  geom_point() +
  guides(size = 'none')

^{Created on 2023-03-09 with reprex v2.0.2}