如何使用ggplot2在2x2排列的不同方面添加水平线？

Question

我有一个按面绘制和分隔的数据库。第一行（a 行）的刻面需要 0.5 处的水平线，而第二行（b 行）的刻面需要 1 处的线。在this example 之后，我已经部分实现了我的目标。但是，0.5 和 1 处的水平线出现在所有方面。

library(ggplot2)

#Data
values <- c(0.4, 0.6, 0.9, 1.1)
Column <- c("UW", "LW", "UW", "LW")
Row <- c("a", "a", "b", "b")
DF <- data.frame(Row, Column, values)
DF$Column <- factor(DF$Column,
                 levels = c("UW", "LW"))
DF$Row <- factor(DF$Row,
                 levels = c("a", "b"))

#Auxiliar DF
Target <- c("a", "b")
Lines <- c(0.5, 1)
Lines_in_plot <- data.frame(Target, Lines)
Lines_in_plot$Target <- factor(Lines_in_plot$Target)

#Plot
ggplot(data = DF, aes(y = values)) +
  geom_bar() +
  facet_grid(Row~Column,
             scales = "free") +
  geom_hline(data = Lines_in_plot,
             yintercept = Lines,
             linetype = "dashed",
             color = "red")

此 MWE 运行但显示以下警告消息：

geom_hline(): Ignoring `data` because `yintercept` was provided.

Answer 1

这是您的解决方案：

library(ggplot2)

#Data
values <- c(0.4, 0.6, 0.9, 1.1)
Column <- c("UW", "LW", "UW", "LW")
Row <- c("a", "a", "b", "b")
DF <- data.frame(Row, Column, values)
DF$Column <- factor(DF$Column,
                 levels = c("UW", "LW"))
DF$Row <- factor(DF$Row,
                 levels = c("a", "b"))

#Auxiliar DF
Row <- c("a", "b")
Lines <- c(0.5, 1)
Lines_in_plot <- data.frame(Row, Lines)
Lines_in_plot$Row <- factor(Lines_in_plot$Row)

#Plot
ggplot(data = DF, aes(y = values)) +
  geom_bar() +
  facet_grid(Row~Column,
             scales = "free") +
  geom_hline(data = Lines_in_plot,
             aes(yintercept = Lines),
             linetype = "dashed",
             color = "red")

两个变化：

1. 将 y 截距融入美学
2. 将目标重命名为 Row 以匹配 Facet，以便它知道如何处理它们

Answer 2

要让拦截显示在特定面板中，您需要将facet_grid 中引用的Row 作为Lines_in_plot 中的变量提供。您还需要将yintercept 放入aes 中，以便ggplot 知道为yintercept 引用Lines_in_plot 数据。

...
#Auxiliar DF
Row <- c("a", "b")
Lines <- c(0.5, 1)
Lines_in_plot <- data.frame(Row, Lines)
Lines_in_plot$Row <- factor(Lines_in_plot$Target)

#Plot
ggplot(data = DF, aes(y = values)) +
  geom_bar() +
  facet_grid(Row~Column,
             scales = "free") +
  geom_hline(data = Lines_in_plot,
             aes(yintercept = Lines),
             linetype = "dashed",
             color = "red")