How to prevent xlim from changing the height using geom_curve?

Question

I have the following code:

library(tidyverse)
data_frame(x = 1:5, x1=x+1, c = c('a','a','a','b','b')) %>% 
      ggplot() +
      geom_curve(aes(x = x, xend= x1, y = 0, yend = 0), curvature = -1.3, alpha=.2) +
    facet_wrap(~ c, ncol=1)

but I would like to tweak the limits of the y axis to cut the background area above ~ .1.

I tried to do this:

data_frame(x = 1:5, x1=x+1, c = c('a','a','a','b','b')) %>% 
  ggplot() +
  geom_curve(aes(x = x, xend= x1, y = 0, yend = 0), curvature = -1.3, alpha=.2) +
  facet_grid(c ~ .) +
  ylim(0,.35) +
  facet_wrap(~ c, ncol=1)

but it simply rescales the archs based on the values in ylim. How can I prevent this behavior?

Answer 1

coord_fixed() has arguments that allow you to control precisely what you would like to have here.

See also http://ggplot2.tidyverse.org/reference/coord_fixed.html for reference.

Unfortunately, it is however not possible to use your x and x1 in a dynamic way inside coord_fixed().

As long as you are fine putting absolute values (0.6 and 6.4 below), you can however do something like this:

data_frame(x = 1:5, x1 = x+1, c = c('a','a','a','b','b')) %>%
  ggplot(.) +
  geom_curve(aes(x = x, xend = x1, y = 0, yend = 0), curvature = -1.3, alpha = .2) +
  facet_grid(c ~ .) +
  coord_fixed(ratio = 7, xlim = c(0.6, 6.4), ylim = c(0, 0.12), expand = FALSE) +
  scale_y_continuous(breaks = c(0, 0.1))

Assuming this looks like what you would want it to look like, note that I set expand = FALSE to start ylim at zero, and added buffers to xlim (0.4) and the upper bound of ylim.
I have modified the default ratio value from 1 to 7, to scale you back down from the 0.7 to 0.1, which is what I understand you would like to have in the end. ratio = 1 would imply that you have the same scale (same distances) on the y-axis as on the x-axis (which is what you refer to as re-scaling I believe).

Finally I had to add the manual breaks for the y-axis (to have fewer ones), such that the grid boxes would be a bit larger, which again is just what I infer as your possible wish.