Yeah, this is an unfortunate consequence when stats and geoms share an aesthetic or parameter name. Fixing this will be surprisingly difficult I'm afraid

Is it because width can be used to set binwidth in stat_summary_bin? Or does width affect something else?

hum... that was my thinking writing this, but now I'm not so sure 😬

I'll have to dig in a bit more when I sit down to fix the issue

If it is any help, I could try to dig for the reason. I don't think that I am at the level of actually writing a fix, but maybe I could find out what is causing it...

That is very welcome 🙏

Ah, I can see where things run into each other. stat_summary_bin does not take a width paramater or aesthetic, but it does calculate one based on the given bins/binwidth argument (or its default). Since that is now present in the data given to geom_errorbar it takes precedence over the provided width parameter...

So, my initial hunch was correct, it was just a bit more complicated. I'm afraid we don't have a great solution for this at the moment. I'll keep this issue open to remind us to think about it

You can use after_stat() to work around this limitation.

library(ggplot2)

iris |>
  ggplot(aes(x = Sepal.Length, y = Sepal.Width, color = Species)) +
  stat_summary_bin(
    aes(width = after_stat(1)),
    geom = "errorbar"
  )
#> No summary function supplied, defaulting to `mean_se()`
#> No summary function supplied, defaulting to `mean_se()`
#> No summary function supplied, defaulting to `mean_se()`

^{Created on 2024-03-28 with reprex v2.1.0}

Should a parameter width override the width column in the data? For basically any other aesthetic given as a parameter, say colour = "red", we override any colour variable passed through aes() or computed by the stat.

It is also a bit verbose the throw the warning about the summary function 3 times