如何手动指定ggplot堆叠条形图的堆叠顺序（从下到上）

需求 #

将堆叠条形图的堆叠顺序从下到上设置为：Epidural、Subdural、Subarachnoid、Intracerebral、Unspecified

当前代码 #

ggplot(cat, aes(x = headbleed_trauma_primary, y = perc, fill = headbleed_category_primary))+
  geom_bar(stat = "identity", position = "stack") + 
  theme_classic()

当前数据框 #

structure(list(headbleed_trauma_primary = c("Nontraumatic", "Nontraumatic", 
"Nontraumatic", "Nontraumatic", "Nontraumatic", "Traumatic", 
"Traumatic", "Traumatic"), headbleed_category_primary = c("Epidural", 
"Intracerebral", "Subarachnoid", "Subdural", "Unspecified", "Epidural", 
"Subarachnoid", "Subdural"), n = c(15L, 2848L, 1113L, 1295L, 
589L, 141L, 2078L, 3477L), perc = c(0.129802699896158, 24.6452059536172, 
9.63136033229491, 11.2062997577016, 5.0969193492558, 1.22014537902388, 
17.9820006922811, 30.0882658359294)), row.names = c(NA, -8L), class = "data.frame")

解决方案 #

ggplot的堆叠顺序由填充变量的因子水平顺序决定，默认从下到上对应因子levels的顺序。只需将headbleed_category_primary转换为指定顺序的因子即可：

1. 转换因子顺序：

cat$headbleed_category_primary <- factor(cat$headbleed_category_primary,
                                         levels = c("Epidural", "Subdural", "Subarachnoid", "Intracerebral", "Unspecified"))

2. 运行原绘图代码，即可得到符合要求的堆叠顺序。

完整代码如下：

# 转换因子顺序
cat$headbleed_category_primary <- factor(cat$headbleed_category_primary,
                                         levels = c("Epidural", "Subdural", "Subarachnoid", "Intracerebral", "Unspecified"))

# 绘制堆叠条形图
ggplot(cat, aes(x = headbleed_trauma_primary, y = perc, fill = headbleed_category_primary))+
  geom_bar(stat = "identity", position = "stack") + 
  theme_classic()

内容的提问来源于stack exchange，提问作者ltong