正如MrFlick所说，您可以使用position = "fill"来填充整个堆叠条形图。（DSC）占据了条形图的大部分，您可能只想为特定组绘制geom_text()，就像你的示例条形图一样，我通过为所有组设置geom_text()来实现这一点，但只允许一个组（carb == 4）使用alpha可见。

library(tidyverse)
library(scales)
data(mtcars)

# calculate percentages, put into dataframe
df <- mtcars %>%
  mutate(carb = factor(carb)) %>% mutate(gear = factor(gear)) %>%
  group_by(gear, carb) %>%
  summarize(n = n()) %>%
  mutate(freq = n / sum(n)) %>%
  mutate(per = label_percent()(freq))  # from the scales package

ggplot(df, aes(x = gear, fill = carb)) +
  geom_bar(position = "fill") +
  geom_text(aes(label = per), 
            stat = "count",
            alpha = ifelse(df$carb == "4", 1, 0), # conditional transparency for geom_text
            position = position_fill(vjust = 0.5))