如何让ggplot分组柱状图中每组内的柱子按平均任期降序排列？

问题背景 #

我需要创建分组柱状图，展示国防、农业、财政、外交四类内阁部长在政党制、个人制、军事制、君主制四类独裁政体中的平均任期。现有代码生成的图表中，每个政体分组内的柱子顺序固定，需求是让每个分组内的柱子按平均任期降序排列（任期最长的部长柱子排在最前）。

数据集 #

structure(list(minister_type = c("Defense", "Finance", "Foreign Affairs", 
"Agriculture", "Defense", "Finance", "Foreign Affairs", "Agriculture", 
"Defense", "Foreign Affairs", "Finance", "Agriculture", "Defense", 
"Foreign Affairs", "Finance", "Agriculture"), regime_subtype = c("Military", 
"Military", "Military", "Military", "Monarch", "Monarch", "Monarch", "Monarch", 
"Party", "Party", "Party", "Party", "Personal", "Personal", "Personal", "Personal"), 
average_tenure = c(2.60493827160494, 2.48979591836735, 2.33165829145729, 
2.19170984455959, 5.94202898550725, 4.20212765957447, 4.14772727272727, 
3.35576923076923, 4.93292682926829, 4.60164835164835, 3.91704035874439, 
3.49769585253456, 3.46043165467626, 2.99093655589124, 2.78651685393258, 
2.57228915662651)), row.names = c(NA, -16L), class = "data.frame")

原代码 #

# Create the grouped bar plot
ggplot(sorted_df, aes(x = regime_subtype, y = average_tenure, fill = minister_type)) +
  geom_bar(stat = "identity", position = "dodge") +
  scale_fill_manual(values = minister_colors) +
  labs(x = "Regime Subtype", y = "Average Tenure", fill = "Minister Type") +
  ggtitle("Average Tenure by Minister Type and Regime Subtype") +
  theme_minimal()

解决方案 #

核心是为每个政体分组生成按任期降序排列的部长类型因子，让ggplot按因子水平顺序绘制柱子。

1. 数据预处理（生成排序后的因子） #

使用dplyr分组排序，创建带顺序的因子列：

library(dplyr)
library(ggplot2)

# 加载数据（替换为你的数据框）
df <- structure(...) # 这里放入上述数据集代码

# 分组排序并生成有序因子
sorted_df <- df %>%
  group_by(regime_subtype) %>%
  arrange(desc(average_tenure), .by_group = TRUE) %>%
  mutate(minister_ordered = factor(minister_type, levels = unique(minister_type))) %>%
  ungroup()

2. 修改绘图代码 #

替换填充变量为有序因子，调整柱子对齐：

# 定义颜色映射（可根据需求修改）
minister_colors <- c("Defense" = "#1f77b4", "Finance" = "#ff7f0e", "Foreign Affairs" = "#2ca02c", "Agriculture" = "#d62728")

# 绘制排序后的分组柱状图
ggplot(sorted_df, aes(x = regime_subtype, y = average_tenure, fill = minister_ordered)) +
  geom_bar(stat = "identity", position = position_dodge(width = 0.9)) +
  scale_fill_manual(values = minister_colors, name = "Minister Type") +
  labs(x = "Regime Subtype", y = "Average Tenure") +
  ggtitle("Average Tenure by Minister Type and Regime Subtype") +
  theme_minimal()

关键说明 #

• group_by() + arrange(.by_group = TRUE)：确保每个政体分组内按任期降序排列
• mutate(factor(...))：将每个分组内的部长类型按排序后的顺序设置为因子水平，ggplot会遵循此顺序绘制柱子
• position_dodge(width = 0.9)：手动指定柱子间距，避免分组内柱子错位

内容的提问来源于stack exchange，提问作者w5698