add stat_manual example

[EvaMaeRey]

I think it would be nice to add a dplyr example that doesn't make use of the args argument like:

xyends_at_means <- function(data){data |> mutate(xend = mean(x, na.rm = T, yend = mean(y, na.rm = T)}

ggplot(mtcars) + 
aes(x = wt, mpg,
color = factor(cyl)) + 
geom_point() + 
stat_manual(geom = "segment", 
                      fun =  xyends_at_means)

Or replace one of the existing examples - I think there are 2 examples that both use dplyr + args+vars.

[teunbrand]

There is already the make_hull() example, what new thing would the dplyr example teach about using stat_manual()?

[EvaMaeRey]

I just think it might sit differently with people. I second guessed if the above would even work given the two examples that showed the dplyr+args+vars, then I felt like that was the correct/only path when using dplyr/tidyr, and maybe I'm still wondering it is the more correct/safe way. 😅

[teunbrand]

If the examples show that you can use a custom function, why wouldn't that also apply to a custom function using dplyr pipes?
I just don't want to spend example real-estate to duplicate things.