如何在ggplot的X轴下方及X、Y轴标题旁添加箭头？

问题 #

需要在ggplot绘制的图表中实现以下效果：

• 在X轴下方添加箭头
• 在X轴标题和Y轴标题旁添加箭头
  当前使用的ggplot代码如下：

quadrant <- ggplot(quadrants, aes(x=Ampolla, y=Energia, label=Branca_percIPI))+
  coord_fixed() +
  coord_cartesian(clip = 'off') +
  scale_x_continuous(expand = c(0, 0), limits = c(-5, 50)) +
  scale_y_continuous(expand = c(0, 0), limits = c(0,50))+
   geom_vline(xintercept = 11.3, color = "grey50", size=1.2) +
   geom_hline(yintercept = 17.7, color = "grey50", size=1.2) +
  geom_text_repel(size = 7,
                   colour = "#2896BA",
                   min.segment.length = Inf, hjust="right", nudge_x=0.9, nudge_y=1.5, force=1,
                  arrow = arrow(length=unit(0.5,"cm"), ends="first"), lineheight = 1)+
  geom_point(colour="#2896BA", size=3.5)+
  labs(title = "Incidència dels colls d'ampolla i dependència energètica total",
       subtitle="(% de variació interanual de l'IPI*, % d'empreses afectades pels colls d'ampolla i % de dependència energètica)",
       x = "Colls d'ampolla (% d'empreses afectades)**",
       y = "Dependència energètica total (%)")+
  annotation_custom(segmentsGrob(c(0.3, -0.1), c(-0.085, 0.28), 
                                 c(1, -0.1), c(-0.085, 0.28), gp = gpar(lwd = 2),
                                 arrow = arrow(length = unit(2.5, 'mm'))))

解决方案 #

通过annotation_custom结合grid包的segmentsGrob可精准控制箭头位置，配合已开启的coord_cartesian(clip = 'off')，就能让图表外的箭头正常显示。以下是调整后的完整代码：

library(ggplot2)
library(grid)

quadrant <- ggplot(quadrants, aes(x=Ampolla, y=Energia, label=Branca_percIPI))+
  coord_fixed() +
  coord_cartesian(clip = 'off') +
  scale_x_continuous(expand = c(0, 0), limits = c(-5, 50)) +
  scale_y_continuous(expand = c(0, 0), limits = c(0,50))+
  geom_vline(xintercept = 11.3, color = "grey50", size=1.2) +
  geom_hline(yintercept = 17.7, color = "grey50", size=1.2) +
  geom_text_repel(size = 7,
                  colour = "#2896BA",
                  min.segment.length = Inf, hjust="right", nudge_x=0.9, nudge_y=1.5, force=1,
                  arrow = arrow(length=unit(0.5,"cm"), ends="first"), lineheight = 1)+
  geom_point(colour="#2896BA", size=3.5)+
  labs(title = "Incidència dels colls d'ampolla i dependència energètica total",
       subtitle="(% de variació interanual de l'IPI*, % d'empreses afectades pels colls d'ampolla i % de dependència energètica)",
       x = "Colls d'ampolla (% d'empreses afectades)**",
       y = "Dependència energètica total (%)")+
  # X轴下方的双向箭头
  annotation_custom(segmentsGrob(x0 = 0.05, y0 = -0.08, x1 = 0.95, y1 = -0.08,
                                 gp = gpar(lwd = 2),
                                 arrow = arrow(length = unit(2.5, 'mm'), ends = "both")))+
  # X轴标题上方的箭头（指向标题）
  annotation_custom(segmentsGrob(x0 = 0.5, y0 = -0.12, x1 = 0.5, y1 = -0.09,
                                 gp = gpar(lwd = 2),
                                 arrow = arrow(length = unit(2, 'mm'), ends = "last")))+
  # Y轴标题右侧的箭头（指向标题）
  annotation_custom(segmentsGrob(x0 = -0.08, y0 = 0.5, x1 = -0.05, y1 = 0.5,
                                 gp = gpar(lwd = 2),
                                 arrow = arrow(length = unit(2, 'mm'), ends = "last")))+
  # 调整边距避免箭头被截断
  theme(plot.margin = margin(10, 10, 40, 40))

核心调整说明： #

• segmentsGrob采用归一化坐标（0-1范围，(0,0)对应绘图区左下角，(1,1)对应右上角），修改x0,y0,x1,y1可灵活调整箭头位置
• ends参数控制箭头方向："both"为双向箭头，"last"为单向箭头指向终点
• 新增theme(plot.margin)增大底部和左侧边距，确保箭头不被画布截断

内容的提问来源于stack exchange，提问作者Maria