Consider implementing guides with custom hastables about ggnewscale

[eliocamp]

The original issue is not longer present in the current version of ggnewscale/ggplot2, so this is not really needed now.

library(ggplot2)
library(ggnewscale)

data <- expand.grid(y = 1:4, x = 1:4)
data$z <- c("a", "b")

ggplot(data, aes(x, y)) +
  geom_tile(data = ~.x[.x$x == 1, ], aes(fill = z)) +
  scale_fill_brewer(palette = 1) +
  new_scale_fill() +
  geom_tile(data = ~.x[.x$x == 2, ], aes(fill = z)) +
  scale_fill_brewer(palette = 2) 

^{Created on 2024-07-18 with reprex v2.1.0}