Expand documentation for coord_flip

[wmacnair]

Hello

First of all, I have used ggplot pretty much every working day for I don't know how many years now, so I should use this opportunity to say thank you for the essential package / nice community / responsive authors / all the things that make it great 🤗

In general I find the documentation of ggplot functions good, with good conceptual background and pretty thorough examples. However whenever I try to understand the tricksy bits of coord_flip, I find myself consistently frustrated by the pretty thin coverage. Questions I have wished were answered:

• How does coord_flip interact with facets? i.e. does the facet x match to the flipped or unflipped x aes?
• How does coord_flip interact with scales? i.e. does the scale x match to the flipped or unflipped x aes?
• How does coord_flip interact with axis-related params in theme?
• Do the xlim and ylim parameters in coord_flip refer to the axes before or after the flipping?
• I'm sure there are others...

It would be great to have an expanded Details section for the coord_flip documentation, going over the concepts here. Maybe even a little diagram! It could also be an opportunity to describe some cases where coord_flip doesn't work so well, or common pitfalls.

Thanks again!
Will

[thomasp85]

Thanks - you are right that there are a lot of questions around coord_flip() that could be answered better. One of the reasons for adding support for bidirectional gems was exactly that coord_flip() introduced these ambiguities and we generally advise to simply use the reverse mapping in the geom rather than flipping the coordinate system.

However since we still provide coord_flip() and will continue to do so for a long time we should improve the docs

[teunbrand]

Since we've decided to supersede coord_flip() in favour of bidirectional geoms in #5123, do you still think it is worth polishing the docs?

[slowkow]

@teunbrand In ggplot2 extensions, how can a Geom "know" if the coords have been flipped with coord_flip()?

After studying the ggplot2 code, I am not seeing any way to figure this out. The reason I ask is because this is causing issues for users of ggrepel.

[slowkow]

Nevermind! Sorry for the bother. As I continued to search through old ggplot2 issues, I found one that helps me, thanks to the discussion in the related commit:

• 2a46b3a

flipped <- inherits(coord, "CoordFlip")