geom_point in terms of two 'size' variables

[Mikołaj Bogucki]

Hi, Is there any option to use two variables in parameter size in ggplot function? E.g.

ggplot(mtcars, aes(qsec,drat, size = cyl))+
geom_point()

Obviously it works and size of points depends on cyl variable. But is it any option to add another sizevariable which can use alpha option e.g.variable = mpg. I found sth like that:

ggplot() +
geom_point(data = mtcars, aes(qsec,drat, size = cyl)) +
geom_point(data = mtcars, aes(qsec,drat, size = mpg), alpha = .1, colour = "red")

But when I want to set the size of each variable separately, it is not possible. When there is one size variable normally I use scale_size_contiunous but with two size variables it doesn't work. I know that using scale_size_continuous two times doesn't change anything. It is possible to achieve appropriate graph?

[Brandon Hurr]

My understanding is that only a single scale of each type can be used
in a plot. Much like Highlander, there can only be one.

In your example, it is setting the scale to cover both cyl and mpg.
Your dots are reflecting the data quite well if you ask me. I assume
you want to have the cyl scale and the mpg scale on their own scale so
they show up better. AFAIK, that can't be done. BUT... you could try
rescaling cyl to the mpg scale or vice versa, but then your legend is
kind of junk.

HTH,
B

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