ggplot2: Why stript.text.y not inheriting 'angle' from strip.text when complete theme?

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I want to set the angle of facet labels for vertical axis and I noticed that I have to use set strip.text.y in the theme specifically as it does not seem to inherit if I set the angle at the level of its parent, strip.text, even if complete=TRUE.

Why is that? (Perhaps I'm using an incomplete theme without realizing it?) Using ggplot2 v3.3.3.

The following attempts to set angle=45 doesn't change the default angle rendering.

(p <- ggplot(iris, aes(x=Petal.Length)) + geom_histogram() + facet_grid(rows = vars(Species)))

p + theme(strip.text   = element_text(angle=45))
p + theme(strip.text   = element_text(angle=45), complete=TRUE) #Results in heavier font.

Incomplete theme Complete theme
Why didn't complete=TRUE trigger inheritance?

Had to be specific:

p + theme(strip.text.y = element_text(angle=45)) # Works!

enter image description here

I read the section titled "Complete vs Incomplete (themes)" in the vignette below but that wasn't clear on this issue.
https://cran.r-project.org/web/packages/ggplot2/vignettes/extending-ggplot2.html

facet ggplot2 r
1 Answers

There is a hierarchy for theme elements:

  • strip.text inherits from text
  • strip.text.y inherits from strip.text
  • strip.text.y.left (and right) inherits from strip.text.y.

'Inheritance' in the theme's case means that a child's properties get filled in by the parent's properties, when this property is missing in the child.

If you evaluate theme_get()$strip.text.y with the default theme, you'll see that angle is -90: not missing. So whenever you set something in the parent strip.text, the strip.text.y's angle overrules the parents angle. I think Kara Woo discussed this behaviour in this talk.

As a sidenote, I don't think you ever need to specify complete for normal plotting purposes. It might only be a useful argument for building new themes for a package or something.

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