如何为ggplot2百分比堆叠条形图添加百分比标注？

要给你的堆叠条形图添加百分比标注，核心是先计算每个分组内的占比，再用geom_text将标注放在对应堆叠位置上。以下是修改后的完整代码：

library(ggplot2)
library(dplyr)
library(scales) # 用于格式化百分比显示

n <- 10000

test <- data.frame(value = sample(1:3, size = n, replace = TRUE),
                   grp = sample(c("A", "B", "C"), size = n, replace = TRUE),
                   item = sample(c("Item1", "Item2", "Item3", "Item4", "Item5", "Item6"), size = n, replace = TRUE)) %>%
  mutate(value = as.factor(value))

# 先计算每个(item, grp, value)组合的百分比
test_summary <- test %>%
  group_by(item, grp, value) %>%
  summarise(count = n(), .groups = "drop") %>%
  group_by(item, grp) %>%
  mutate(percent = count / sum(count))

# 绘制带标注的堆叠条形图
test_summary %>%
  ggplot(aes(x = grp, y = percent, fill = value, group = value)) + 
  geom_bar(stat = "identity", position = 'fill') +
  # 添加百分比标注，vjust=0.5让标签居中在堆叠块内
  geom_text(aes(label = percent(percent, accuracy = 1)), 
            position = position_fill(vjust = 0.5), size = 3) +
  facet_wrap(item ~., ncol = 2) +
  coord_flip() +
  scale_fill_manual(values = c("green", "yellow", "red")) +
  scale_y_continuous(labels = percent) # 将y轴刻度转为百分比格式

关键说明： #

• 先用group_by(item, grp, value)统计每个子组的数量，再按item, grp分组计算占比percent
• geom_text的position = position_fill(vjust = 0.5)确保标签垂直居中在每个堆叠块里
• scales::percent()用来将小数格式的占比转为带%符号的文本，accuracy=1控制保留整数百分比
• 把geom_bar的stat显式设为"identity"，因为我们已经提前计算好了y值（百分比）

内容的提问来源于stack exchange，提问作者D. Studer