尝试使用 geom_abline 添加图例

Question

我有一个数据框，保存为df，其中有两列我想绘制的点。另外，我想在情节上绘制两条线，并希望这些线有一个图例。这是我的代码：

ggplot(df, aes(x = x, y = y)) + 
  geom_point(color = "black", shape = 16, alpha = 1) +
  scale_x_continuous(name = "x", limits = c(-5, 5)) + 
  scale_y_continuous(name = "y", limits = c(-5, 5)) +
  geom_abline(intercept = 0, slope = 4/3, linetype = "dashed", 
              color = "gray40", size = 1, aes(colour = "XNULL")) + 
  geom_abline(intercept = 0, slope = 0, linetype = "dotted", 
              color = "gray40", size = 1, aes(colour = "YNULL")) +
  scale_color_manual(name = "", values = c("XNULL" = "red", "YNULL" = "blue")) +
  theme(panel.background = element_rect(fill = "white"),
        panel.border = element_rect(colour = "black", fill = NA, size = 1),
        legend.position = "bottom")

但是，当我运行它时，没有出现图例（我希望在底部显示图例）。关于我做错了什么的任何建议？我是使用 ggplot2 的新手，我在其他论坛上查找的解决方案都没有帮助。

Answer 1

您可以尝试创建另一个 data.frame 来包含有关您的 ablines 的信息：

df = data.frame(x=runif(10),y=runif(10))
df2 = data.frame(intercept=0,slope=c(4/3,0),type=c("XNULL","YNULL"))

然后我们可以调用geom_abline指定aes以便我们可以使用

ggplot(df, aes(x = x, y = y)) + 
geom_point(color = "black", shape = 16, alpha = 1) +
scale_x_continuous(name = "x", limits = c(-5, 5)) + 
scale_y_continuous(name = "y", limits = c(-5, 5)) +
geom_abline(data=df2,aes(intercept=intercept,slope=slope,
linetype=type,col=type),size = 1) +
scale_color_manual(name = "", values = c("XNULL" = "red", "YNULL" = "blue")) +
scale_linetype_manual(name = "", values = c("XNULL" = "dashed", "YNULL" = "dotted")) +
theme(panel.background = element_rect(fill = "white"),
      panel.border = element_rect(colour = "black", fill = NA, size = 1),
legend.position = "bottom")

Answer 2

来自文档：

这些geoms 的行为与其他geoms 略有不同。你可以提供 参数有两种方式：要么作为图层函数的参数， 或通过美学。如果您使用参数，例如geom_abline（截距= 0，slope = 1)，然后geom在幕后制作一个新的数据框 仅包含您提供的数据。

显然，您必须在aes 中指定intercept 和slope，才能正常工作。

library(ggplot2)

ggplot(iris, aes(x = Sepal.Length, y = Sepal.Width)) + 
  geom_point() +
  coord_cartesian(xlim = c(0,10), ylim = c(0,10)) +
  geom_abline(aes(intercept = 0, slope = 0, color = "X"), linetype = "dotted") +
  geom_abline(aes(intercept = 0, slope = 4/3, color = "Y"),linetype = "dashed") +
  scale_color_manual(values = c(X = 'grey', Y = 'black'))

^{由reprex package (v0.3.0) 于 2020-02-12 创建}