标题：如何在ggplot2中在x轴下方画一条带箭头的线？

Question

问题： 我正在尝试在 ggplot2 中创建一个绘图，其中箭头线指向外部，并位于 x 轴下方。我在 ggplot2 中使用了 geom_segment 函数，但它在绘图上绘制。我想要这条线有一个指向右侧的箭头，位于 x 轴下方，标记为左侧内侧和右侧外侧，以表示类似“内部”部分的内容。

这是我到目前为止的代码：

library(tidyr)
library(ggplot2)
library(grid)  # For arrow customization

# Define the vectors
st <- c("a1", "a2", "a3", "a4", "a5", "a6", "a7", "a8", "a9", "a10")
y1 <- c(5, 1, 4, 6, 2, 3, 7, 8, 2, 8)                   # Create more example data
y2 <- c(3, 3, 3, 3, 4, 4, 5, 5, 7, 7)

# Create a data frame
df <- data.frame(st = st, y1 = y1, y2 = y2)

# Pivot from wide to long
df_long <- df %>%
  pivot_longer(
    cols = c("y1", "y2"),  # Columns to pivot
    names_to = "variable",       # Column name for variable names
    values_to = "value"          # Column name for values
  )

# Create the plot
ggplot(data = df_long, aes(x = st, y = value, color = variable, group = variable)) +
  geom_line(size = 1.2) +  # Adjust line thickness
  labs(
    title = "Line Plot with Arrow Beneath X-Axis",
    x = "Identifier",
    y = "Value",
    color = "Variable"
  ) +
  theme_minimal() +  # Use a clean theme for better visualization
  geom_segment(
    aes(x = 1, y = -1, xend = 10, yend = -1),  # Line for "inner" section
    arrow = arrow(type = "closed", length = unit(0.2, "inches")),
    color = "blue",
    size = 1.2
  )  +
  annotate("text", x = 3, y = -1.5, label = "Inner", color = "blue", size = 4) +  # Label for inner
  annotate("text", x = 8, y = -1.5, label = "Outer", color = "red", size = 4)  # Label for outer

我也尝试过这个

+ geom_line(size = 1.2) +  # Adjust line thickness
  geom_hline(yintercept = 0, linetype = "dashed") +  # Add horizontal line at y = 0
  geom_vline(xintercept = -1, linetype = "dashed") +  # Add vertical line at x = 0

但没有在图外的 x 轴下方得到箭头线

请更正我的代码，提前致谢

Answer 1

根据您的代码，一个快速选项是通过

coord_cartesian

设置限制，以便箭头绘制在面板之外。另外设置

clip="off"

并通过增加例如为箭头留出一些空间。绘图的下边距：

library(ggplot2)

ggplot(data = df_long, aes(x = st, y = value, color = variable, group = variable)) +
  geom_line(size = 1.2) + # Adjust line thickness
  labs(
    title = "Line Plot with Arrow Beneath X-Axis",
    x = "Identifier",
    y = "Value",
    color = "Variable"
  ) +
  theme_minimal() + # Use a clean theme for better visualization
  geom_segment(
    aes(x = 1, y = -1.5, xend = 10, yend = -1.5), # Line for "inner" section
    arrow = arrow(type = "closed", length = unit(0.2, "inches")),
    color = "blue",
    size = 1.2
  ) +
  annotate("text", x = 3, y = -2, label = "Inner", color = "blue", size = 4) + # Label for inner
  annotate("text", x = 8, y = -2, label = "Outer", color = "red", size = 4) +
  coord_cartesian(clip = "off", ylim = c(0, NA)) +
  theme(plot.margin = margin(5.5, 5.5, 50, 5.5))