使用scale_fill_binned()时如何使用特定的填充颜色？

我想使用我自己的填充颜色（例如：c("red", "blue", "grey50", "black")) 使用函数时scale_fill_binned()在 ggplot 代码中。我怎样才能做到这一点？

这是一个最小的可重现示例：

library(tidyverse)

dat <- mtcars %>% 
       group_by(cyl) %>% 
       summarise(n = n(),
                 mean_hp = mean(hp)) %>% 
       ungroup

ggplot(data = dat, aes(x = cyl, y = mean_hp, size = n, fill = n)) +
  geom_point(shape = 21) +
  scale_size_binned(breaks = c(8, 10, 12), guide = guide_bins(show.limits = T)) +
  scale_fill_binned(breaks = c(8, 10, 12), guide = guide_bins(show.limits = T), type = "viridis") +
  labs(x = "Cylinder", y = "Mean hp", fill = "Nb of cars", size = "Nb of cars") +
  theme_minimal()

输出如下所示：

要使用这一系列函数，您需要提供一个返回具有类的对象的函数"ScaleContinuous" "Scale" "ggproto" "gg"（即等效输出scale_fill_viridis_c)!

scale_fill_custom <- function (..., alpha = 1, begin = 0, end = 1, direction = 1, 
  option = "D", values = NULL, space = "Lab", na.value = "grey50", 
  guide = "colourbar", aesthetics = "fill") {
  continuous_scale(aesthetics, scale_name = "custom", 
    palette = scales:::gradient_n_pal(c("red", "blue", "grey50", "black"), 
    values, space), na.value = na.value, 
    guide = guide, ...)
}
ggplot(data = dat, aes(x = cyl, y = mean_hp, size = n, fill = n)) +
  geom_point(shape = 21) +
  scale_size_binned(breaks = c(8, 10, 12), guide = guide_bins(show.limits = T)) +
  scale_fill_binned(breaks = c(8, 10, 12), guide = guide_bins(show.limits = T), 
    type = scale_fill_custom) +
  labs(x = "Cylinder", y = "Mean hp", fill = "Nb of cars", size = "Nb of cars") +
  theme_minimal()

请注意，您使用颜色作为尺度，以便通过眼睛将其转换为具有数字意义的差异。颜色是在手动应用的点之间插值的，因此实际上并不是您的确切颜色。如果您希望按颜色对平均值进行划分，最好创建一个因素，然后手动应用您的主题。

ggplot(data = mutate(dat, n = cut(n, breaks = c(0, 8, 10, 12, 20))), 
  aes(x = cyl, y = mean_hp, size = n, fill = n)) +
  geom_point(shape = 21) +
  scale_size_discrete() +
  scale_fill_manual(values = c("red", "blue", "grey50", "black")) +
  labs(x = "Cylinder", y = "Mean hp", fill = "Nb of cars", size = "Nb of cars") +
  theme_minimal()