在R中创建Y轴分层对齐的Alluvial图（保留流量厚度与波形）

需求说明 #

需要创建Alluvial图，满足以下要求：

• 类别在Y轴分层对齐（同类别在两个时间轴上的Y位置对应），解决示例图中Medium→Medium过渡时的个体“下移”视觉问题
• 保留线条厚度对应案例数量的展示
• 保留Alluvial图的波浪形态

解决方案：使用ggalluvial包的对齐参数 #

默认的geom_alluvium采用justify对齐方式，会按数据顺序排布流，导致同类别过渡时出现偏移。通过设置align = "center"参数，可让同类别在两个轴上的Y轴中心位置对齐，消除偏移，同时保留原有视觉特性。

完整代码 #

library(ggplot2)
library(ggalluvial)

# 构建测试数据
df_test <- data.frame(
  ID = 1:11,
  T1 = c("Low", "Very high", "Medium", "Low", "High", "Medium", "High", "Medium", "Low", "High", "Low"),
  T2 = c("High", "High", "Medium", "Very high", "High", "High", "Medium", "High", "Medium", "High", "Low")
)

# 设置类别层级，确保前后时间点的类别顺序统一
cat_levels <- c("Very high","High",  "Medium", "Low")
df_test$T1 <- factor(df_test$T1, levels = cat_levels)
df_test$T2 <- factor(df_test$T2, levels = cat_levels)

# 创建分层对齐的Alluvial图
ggplot(df_test, aes(axis1 = T1, axis2 = T2)) +
  # 核心：设置align = "center"实现同类别Y轴对齐，保留波浪形态和厚度
  geom_alluvium(aes(fill = T1), width = 1/12, stat = "alluvium", align = "center") +
  geom_stratum(width = 1/5) +
  geom_text(stat = "stratum", aes(label = after_stat(stratum)), size = 3) +
  scale_x_discrete(limits = c("T1", "T2")) +
  scale_fill_manual(values = c("Low" = "skyblue",
                               "Medium" = "orange",
                               "High" = "red",
                               "Very high" = "darkred")) +
  labs(title = "分类从T1到T2的过渡（分层对齐版）",
       x = "时间点",
       y = "个体数量",
       fill = "状态") +
  theme_minimal() +
  theme(axis.text.x = element_text(face = "bold", size = 14),
        axis.text.y = element_blank(),
        axis.ticks.y = element_blank(),
        panel.grid.major.y = element_blank())

关键说明 #

• align = "center"：让每个类别在两个轴上的Y轴中心位置保持一致，确保同类别过渡的流垂直对齐，消除偏移
• 线条厚度自动对应案例数量：geom_alluvium会根据每个过渡组的个体数自动调整线条粗细
• 波浪形态保留：默认的geom_alluvium会维持平滑的波浪路径，无需额外设置

内容的提问来源于stack exchange，提问作者Oscar Kjell