基于R语言ggforce包geom_arc_bar绘制分组学科均值环形图方法咨询

步骤1：数据预处理 #

首先需要先将宽表数据转为长表，再计算每个分组对应四门学科的平均成绩：

# 加载所需包
library(tidyverse)
# 示例数据，固定随机种子方便复现结果
set.seed(123)
df <- data.frame(English = sample(1:100,10),
                 Math = sample(1:100,10),
                 History = sample(1:100,10),
                 Science = sample(1:100,10),
                 Group = rep(c("A","B","C","D","E"),each=2))
# 宽表转长表+计算分组学科均值
df_mean <- df %>%
  pivot_longer(cols = -Group, names_to = "Subject", values_to = "Score") %>%
  group_by(Group, Subject) %>%
  summarise(mean_score = mean(Score), .groups = "drop")

方案1：使用ggforce包的geom_arc_bar实现 #

匹配你提到的实现函数，逻辑更直观：

# 提前安装包：install.packages("ggforce")
library(ggforce)
# 补充绘图所需的角度、半径参数
df_arc <- df_mean %>%
  mutate(
    # 四门学科均分2π圆周，每门占π/2弧度，分配起始/结束弧度
    start = case_when(
      Subject == "English" ~ 0,
      Subject == "Math" ~ pi/2,
      Subject == "History" ~ pi,
      Subject == "Science" ~ 3*pi/2
    ),
    end = start + pi/2,
    # 给分组分配环形内外半径，从内到外依次为A/B/C/D/E组
    group_num = as.numeric(factor(Group, levels = c("A","B","C","D","E"))),
    r0 = group_num * 0.7, # 环形内半径
    r = r0 + 0.6 # 环形外半径
  )
# 绘图
ggplot() +
  geom_arc_bar(data = df_arc,
               aes(x0 = 0, y0 = 0, r0 = r0, r = r, 
                   start = start, end = end, fill = Subject,
                   alpha = mean_score)) +
  coord_fixed() + # 固定坐标轴比例避免环形变形
  # 添加分组标签
  annotate("text", x = 0, y = c(1,1.7,2.4,3.1,3.8), 
           label = c("A组","B组","C组","D组","E组"), size = 3) +
  scale_fill_brewer(palette = "Set2") +
  labs(fill = "学科", alpha = "平均成绩") +
  theme_void() # 清空多余背景元素

注：如果需要弧长而非透明度对应均值大小，只需把end参数修改为end = start + (mean_score/100)*pi/2即可，此时每个学科的弧长会和成绩成正比。

方案2：ggplot2原生实现（无需安装ggforce） #

使用原生geom_rect配合极坐标也可实现同等效果：

# 补充绘图参数
df_polar <- df_mean %>%
  mutate(
    # 学科对应x轴区间
    subject_num = as.numeric(factor(Subject, levels = c("English","Math","History","Science"))),
    xmin = subject_num - 1,
    xmax = subject_num,
    # 分组对应y轴区间
    group_num = as.numeric(factor(Group, levels = c("A","B","C","D","E"))),
    ymin = group_num * 2 - 1.5,
    ymax = group_num * 2 - 0.5
  )
# 绘图
ggplot(df_polar) +
  geom_rect(aes(xmin = xmin, xmax = xmax, 
                ymin = ymin, ymax = ymax, 
                fill = Subject, alpha = mean_score)) +
  coord_polar(theta = "x") + # 转极坐标，x轴对应圆周方向
  # 设置x轴刻度为学科名称
  scale_x_continuous(breaks = c(0.5,1.5,2.5,3.5),
                     labels = c("English","Math","History","Science")) +
  # 设置y轴刻度为分组名称
  scale_y_continuous(breaks = c(1,3,5,7,9),
                     labels = c("A组","B组","C组","D组","E组")) +
  scale_fill_brewer(palette = "Set2") +
  labs(fill = "学科", alpha = "平均成绩", x = "", y = "") +
  theme_bw() +
  theme(panel.grid = element_blank())

如果需要弧长对应成绩，把xmax参数修改为xmax = xmin + (mean_score/100)即可。

内容的提问来源于stack exchange，提问作者Jeff238