Misleading noise when using geom_jitter in combination with facet_wrap

[hkosm]

Hello,

I like to use geom_jitter mostly to plot discrete data and avoid overplotting.

When using a combination of geom_jitter and facet_wrap with free scales I came to the issue that due to the free scales, jittering appeared misleading.

In the example below, I would like to see approximately equal noise, as I use jittering purely for visibility of data points. Apparently though, due to the free scales in geom_wrap the jittering looks different in the two facets.
How could this be approached? Could this be an issue inside face_wrap?

library(ggplot2)

set.seed(123)
df <- data.frame(
  y = rnorm(100, 50, 10),
  x = c(rep(1:5, 10), rep(seq(0, 100, length.out = 5), 10)),
  group = c(rep("a", times = 50), rep("b", times = 50))
)

ggplot(df, aes(x = x, y = y)) +
  geom_point(color = "orange", alpha = 0.7) +
  geom_point(position = "jitter", color = "blue", alpha = 0.7) +
  facet_wrap( ~ group, scales = "free")

^{Created on 2020-01-10 by the reprex package (v0.3.0)}

[yutannihilation]

Thanks. The default jitterings are calculated on the whole data, not on the data per PANEL. It seems it's possible to delay the calculation to compute_layer() so that PANEL in data can be considered. (But, I'm not yet sure which behaviour is semantically correct)

ggplot2/R/position-jitter.r

Lines 67 to 80 in 3e3abd9

	setup_params = function(self, data) {
	list(
	width = self$width %||% (resolution(data$x, zero = FALSE) * 0.4),
	height = self$height %||% (resolution(data$y, zero = FALSE) * 0.4),
	seed = self$seed
	)
	},
	compute_layer = function(self, data, params, layout) {
	trans_x <- if (params$width > 0) function(x) jitter(x, amount = params$width)
	trans_y <- if (params$height > 0) function(x) jitter(x, amount = params$height)
	with_seed_null(params$seed, transform_position(data, trans_x, trans_y))
	}