stat_binhex, stat_summary_hex, and ggplot2's bins are out of kilter

[AmagicalFishy]

library(ggplot2)
dat <- data.frame(x = rnorm(100000, 0, 5), y = rnorm(100000, 0, 5), z = rnorm(100000, 42, 42))

hexHist = ggplot(dat, aes(x, y, z = z)) + 
    stat_binhex(bins = 10) +
    stat_summary_hex(aes(label=..value..), bins = 10,
                     fun = function(z) {
                         (round(sum(z)/length(z), 0))
                     },
                     geom = "text")

And, if we look at the bin centers of ggplot_build():

hexDat = ggplot_build(hexHist)$data[[1]] 
hexHist2 = hexHist + annotate("text", hexDat$x, hexDat$y, label = "o")

I've been told that some tiles that are supposed to be there aren't being plotted.

[hadley]

Simpler reprex:

set.seed(12)
n <- 1e4
dat <- data.frame(x = rnorm(n, 0, 5), y = rnorm(n, 0, 5))

ggplot(dat, aes(x, y, z = x)) + 
  stat_binhex(bins = 10) +
  stat_summary_hex(bins = 10, fun = length,  geom = "point", colour = "red")

Not only are points misaligned, some coloured cells don't have red points and vice versa.

[hadley]

Even simpler, and calibrated with geom_point(): suggests that the bug is in stat_summary_hex():

set.seed(12)
n <- 1e2
dat <- data.frame(x = rnorm(n, 0, 5), y = rnorm(n, 0, 5))

ggplot(dat, aes(x, y, z = x)) + 
  stat_binhex(bins = 10) + 
  geom_point(colour = "white") + 
  guides(fill = "legend")

ggplot(dat, aes(x, y, z = x)) + 
  stat_binhex(bins = 10) +
  stat_summary_hex(bins = 10, fun = length,  geom = "point", colour = "red")