ggplot2: Flip axes and maintain aspect ratio of data

Question

In ggplot2, the coord_fixed() coordinate system ensures that the aspect ratio of the data is maintained at a given value. So, the shape of the panel changes to maintain the shape of the data. Meanwhile coord_flip() swaps the axes of the plot. However, a plot in ggplot2 must have exactly one coordinate system, so these functions cannot be combined.

My question is:

Does there exist a way to combine the behaviours of coord_fixed() and coord_flip(), resulting in a coordinate system with the x and y axes exchanged and a fixed aspect ratio of the data?

This is a popular question, however the common answer is incorrect:

• How do I to fix aspect ratio and apply coord_flip in ggplot2?
• Flipping and maintaining aspect ratio of a chart in ggplot2

The commonly suggested answer is to use coord_flip() together with theme(aspect.ratio = 1) instead of coord_fixed(). However, as per the ggplot2 documentation, this setting refers to the "aspect ratio of the panel." Thus, the data will change shape to maintain the shape of the panel.

I suspect that this is a feature that does not currently exist in ggplot2. But more importantly I think that a correct solution or at least response to this question should be documented.

Quick minimal example of the issue:

library(ggplot2)
x <- 1:100; data <- data.frame(x = x, y = x * 2)
p <- ggplot(data, aes(x, y)) + geom_point()

p # by default panel and data both fit to device window
p + coord_fixed() # panel changes shape to maintain shape of data
p + theme(aspect.ratio = 1) # data changes shape to maintain shape of panel
p + coord_fixed() + coord_flip() # coord_flip() overwrites coord_fixed()

# popular suggested answer does not maintain aspect ratio of data:
p + coord_flip() + theme(aspect.ratio = 1)

Answer 1

I agree that the theme solution isn't really a proper one. Here is a solution that does work programatically by calculating the aspect from the actual axes ranges stored in the plot object, but it takes a few lines of code:

ranges <- ggplot_build(p)$layout$panel_ranges[[1]][c('x.range', 'y.range')]
sizes <- sapply(ranges, diff)
aspect <- sizes[1] / sizes[2]

p + coord_flip() + theme(aspect.ratio = aspect)

The solution I would probably use in practice, is to use the horizontal geoms in the ggstance package (although this may not always be feasible).

Note: This will only give the exact correct answer for two continuous scales with an equal multiplicative extend argument (i.e. the default).

edit: In many cases I would recommend using coord_equal combined with the ggstance package instead of this solution.

Answer 2

I ended up just flipping the x and y arguments in the aes specification. So for example instead of:

ggplot(mtcars,aes(x=wt,y=drat))+geom_point()+coord_fixed()

I did:

ggplot(mtcars,aes(x=drat,y=wt))+geom_point()+coord_fixed()