Symbol not shown for manually added values in the legend

[julou]

Hello,

This might be related to #3372.
I need to combine several plots in a grid and make one shared legend. For this, I used to set manually the legend values and limits in the colour scale. But it doesn't work anymore

Here is a reprex:

ggplot(mpg, aes(class, hwy, col=class)) + 
  geom_boxplot() +
  scale_color_manual(values=c("suv"="blue", "compact"="red", "pickup"="green", "foo"="orange", "bar"="pink"), 
                     limits=c("suv", "compact", "pickup", "foo", "bar") )

The levels are added to the legend ("foo" and "bar") but the corresponding symbols are not shown.

I tried (man many other things) adding a blank geom but it didn't help (same output).

ggplot(mpg, aes(class, hwy, col=class)) + 
  geom_boxplot() +
  geom_blank(data=~mutate(., class=fct_recode(class, "foo"="compact", "bar"="pickup"))) +
  scale_color_manual(values=c("suv"="blue", "compact"="red", "pickup"="green", "foo"="orange", "bar"="pink"), 
                     limits=c("suv", "compact", "pickup", "foo", "bar") )

This used to be with previous version of ggplot2 (3.4.1 on top of my head), but does not anymore with 3.5.1.
Thank you in advance for your guidance.

[teunbrand]

Thanks for the report! You're right that this is a recent change, but it is a deliberate one. The keys are not shown is because no layer is representing the foo/bar levels. The way to force these non existing levels to show up with little boxplot keys is to use geom_boxplot(show.legend = TRUE). This has been reported before in #5728 and we have no intention of reverting the change, so I'm going to close this issue.

[julou]

Thanks a lot for the quick answer! I'm glad to ready that this case is covered. I realise that I should have filed it as a support request.

If someone reads the initial post and wonders, here is the working example:

ggplot(mpg, aes(class, hwy, col=class)) + 
  geom_boxplot(show.legend=TRUE) +
  scale_color_manual(values=c("suv"="blue", "compact"="red", "pickup"="green", "foo"="orange", "bar"="pink"), 
                     limits=c("suv", "compact", "pickup", "foo", "bar") )

[teunbrand]

I realise that I should have filed it as a support request

We'd prefer it if people go to venues specialised in providing support, like stack overflow or the Posit community. This here issue tracker is used to report bugs and file feature requests.

[julou]

I understand that, but you probably also realise that this is not always obvious to a user whether a breaking change is a bug or a design choice. And my google fu was not strong enough to spot any of the link you mention in the other issue (https://github.com/tidyverse/ggplot2/issues/5728#issuecomment-1970036164)…
Apologies… and thanks again in any case!