如何在ggplot2的geom_point上叠加半圆展示双重病毒感染数据？

问题背景 #

需要生成点图展示多个个体随时间的病毒感染变化：不同病毒用不同颜色区分；同一时间点感染多种病毒时，第二种病毒以半圆（Unicode字符\u25D7）叠加在第一个病毒的点上。当前遇到两个问题：

1. Unicode字符无法正常显示，仅出现空心方块
2. 需要隐藏Res2中的"Neg"类别，仅在同时检测到两种病毒时显示半圆

环境：R v4.4.0，Windows 10，编码为English_United States.utf8

解决方案 #

1. 仅在同时感染时显示半圆（过滤Res2的"Neg"） #

在第二层geom_point中通过subset参数过滤掉Res2为"Neg"的行，只保留存在第二种病毒的记录，避免无效绘图。

2. 解决Unicode字符显示问题 #

Windows系统默认字体可能不支持部分Unicode字符，使用showtext包加载支持完整Unicode的字体（如微软雅黑、Noto Sans等），确保字符正常渲染。

修改后的完整代码 #

library(ggplot2)
library(ggthemes)
library(dplyr)
library(showtext)

# 加载支持Unicode的字体（Windows下微软雅黑路径示例，可替换为其他支持字体）
font_add("msyh", "msyh.ttc")
showtext_auto()

# 示例数据
AnimalID <- c("A","A","A","A","A","B","B","B","B","B","C","C","C","C","C")
Week <- c(1,2,3,4,5,1,2,3,4,5,1,2,3,4,5)
Res1 <- c("HV1","HV1","Neg","HV2","Neg","Neg","HV2","HV1","HV1","HV1","HV1","HV1","HV2","Neg","HV1")
Res2 <- c("HV2","Neg","Neg","Neg","Neg","Neg","Neg","HV2","Neg","Neg","Neg","HV2","Neg","Neg","Neg")
AllHV <- c("HV1 and HV2","HV1","Neg","HV2","Neg","Neg","HV2","HV1 and HV2","HV1","HV1","HV1","HV1 and HV2","HV2","Neg","HV1")

db <- data.frame(AnimalID, Week, Res1, Res2, AllHV)

# 绘制图形
Exgraph <- ggplot(db, aes(x = Week, y = AnimalID, color = Res1)) + 
  geom_point(size = 3, shape = 16) +
  # 仅在Res2不为Neg时绘制半圆，形状设为Unicode字符，大小略大于底层点
  geom_point(data = subset(db, Res2 != "Neg"), 
             aes(x = Week, y = AnimalID, color = Res2),
             shape = "\u25D7", size = 4) +
  theme_tufte() +
  ggtitle("HV Shedding Patterns") +
  xlab("Study Week") +
  ylab("Animal ID") +
  theme(axis.line = element_line(colour = "black")) +
  theme(plot.title = element_text(face = "bold", size = 18, family = "msyh")) +
  theme(axis.text = element_text(size = 10, family = "msyh")) +
  theme(axis.title = element_text(face = "bold", size = 14, family = "msyh")) +
  theme(legend.title = element_text(size = 14, face = "bold", family = "msyh"),
        legend.text = element_text(size = 11, family = "msyh")) +
  labs(color = "HV") +
  scale_color_manual(values = c("green", "blue", "grey80"))

Exgraph

关键说明 #

• 过滤数据：通过subset(db, Res2 != "Neg")精准筛选出同时感染两种病毒的时间点，避免Res2为"Neg"时的无效绘图操作。
• 字体设置：showtext包让R调用系统中支持Unicode的字体，彻底解决空心方块问题；需在theme中指定字体family，保证标题、坐标轴等所有文本统一使用该字体。
• 形状大小：将半圆的size设为4（略大于底层点的size=3），确保半圆能清晰覆盖底层点，同时不遮挡病毒颜色标识。

内容的提问来源于stack exchange，提问作者TurtleyAwesome