从使用 2 个不同几何图形创建的 ggplot 图例中删除某些值

Question

我制作了一个 ggplot 图，其中的图例是由来自 2 个不同几何图形的映射制成的，如下所示：

# Create data.frame with shading info
shading <- data.frame(min = seq(from = 0.5, to = max(as.numeric(as.factor(mtcars$carb))), by = 1),
                      max = seq(from = 1.5, to = max(as.numeric(as.factor(mtcars$carb))) + 0.5, by = 1),
                      col = c(0,1))

# Plot
ggplot() +
  geom_col(data = mtcars, mapping = aes(x = factor(carb), y = mpg, fill = factor(cyl))) +
  geom_rect(data = shading,
            aes(xmin = min, xmax = max, ymin = -Inf, ymax = Inf,
                fill = factor(col)), alpha = 0.3) +
  scale_fill_manual(values = c("black", "white", "green", "blue", "red")) +
  geom_col(data = mtcars, mapping = aes(x = factor(carb), y = mpg, fill = factor(cyl))) 

如何从图例中删除前 2 个图例项（黑色 0 和白色 1）但将其保留在图表上？

谢谢

Answer 1

您可以在scale_fill_manual() 调用中明确设置中断 - 这允许您说出哪些将被标记，哪些不会被标记。 （我在这里保留了剩余的代码）。如果您正在寻找更多信息和演练：https://luisdva.github.io/rstats/set-the-breaks/

library(ggplot2)
shading <- data.frame(min = seq(from = 0.5, to = max(as.numeric(as.factor(mtcars$carb))), by = 1),
                      max = seq(from = 1.5, to = max(as.numeric(as.factor(mtcars$carb))) + 0.5, by = 1),
                      col = c(0,1))

# Plot
ggplot() +
  geom_col(data = mtcars, mapping = aes(x = factor(carb), y = mpg, fill = factor(cyl))) +
  geom_rect(data = shading,
            aes(xmin = min, xmax = max, ymin = -Inf, ymax = Inf,
                fill = factor(col)), alpha = 0.3) +
  scale_fill_manual(values = c("black", "white", "green", "blue", "red"),
                    # Adding breaks
                    breaks = c(4, 6, 8)) +
  geom_col(data = mtcars, mapping = aes(x = factor(carb), y = mpg, fill = factor(cyl))) 

^{由reprex package (v0.3.0) 于 2020 年 7 月 28 日创建}

Answer 2

一个非常直接的选择是简单地使用两个比例来填充。

library(ggplot2)
library(ggnewscale)
#> Warning: package 'ggnewscale' was built under R version 4.0.2
shading <- data.frame(min = seq(from = 0.5, to = max(as.numeric(as.factor(mtcars$carb))), by = 1),
                      max = seq(from = 1.5, to = max(as.numeric(as.factor(mtcars$carb))) + 0.5, by = 1),
                      col = c(0,1))

ggplot() +
  geom_col(data = mtcars, mapping = aes(x = factor(carb), y = mpg, fill = factor(cyl)))+
  scale_fill_manual(values = c( "green", "blue", "red")) +
  new_scale_fill() +
  geom_rect(data = shading,
            aes(xmin = min, xmax = max, ymin = -Inf, ymax = Inf,
                fill = factor(col)), alpha = 0.3, show.legend = FALSE) +
  scale_fill_manual(values = c("black", "white"))

^{由reprex package (v0.3.0) 于 2020 年 7 月 28 日创建}