In a `facet_wrap`ed grid, center subplots at 0 while keeping `free_x`

Question

In the plot below, I have a faceted grid.

Is there any way to center both subplots at 0, while keeping different min/max values for the x axis?

In the case below that would be xlim=c(-1,1) for left and xlim=c(-2,2) for right, but it should be generally applicable.

(in a real life example, those are faceted volcano plots and I want to center at 0 effect size but keep the different x scales for different plots)

library(ggplot2)
df = data.frame(x=c(1,2), y=c(0,0), group=c(1,2))
ggplot(df, aes(x=x, y=y)) + geom_point() + facet_wrap(~group, scale="free_x")

Answer 1

I've also needed something like this to display asymmetric spectra side-by-side,

Try this function,

symmetrise_scale <- function(p, axis = "x"){
  gb <- ggplot_build(p)
  type <- switch(axis, "x" = "x.range", "y" = "y.range")
  lims <- sapply(gb$panel$ranges, "[[", type)
  fname <- as.character(p$facet$facets)
  facets <- gb$panel$layout[[fname]]
  lims2 <- as.vector(t(tcrossprod(apply(abs(lims), 2, max), c(-1,1))))
  dummy <- setNames(data.frame(rep(facets, each=2), lims2), c(fname, axis))
  switch(axis, 
         "x" = p + geom_blank(data=dummy, aes(x=x, y=Inf), inherit.aes = FALSE), 
         "y" = p + geom_blank(data=dummy, aes(x=Inf, y=y), inherit.aes = FALSE))
}


library(ggplot2)
df = data.frame(x=c(1,2), y=c(5,0.2), group=c(1,2))
p <- ggplot(df, aes(x=x, y=y)) + geom_point() + facet_wrap(~group, scale="free")
symmetrise_scale(p, "x")

symmetrise_scale(p, "y")