如何在ggplot的Alluvial图中调整Stratum分层框的边框线宽？

问题说明 #

使用ggplot结合ggalluvial绘制Alluvial图时，分层框（stratum）辨识度不足，希望在不修改颜色设置的前提下，仅增大左右两侧分层框的边框线宽，不调整框之间连接线的宽度。

原绘图代码 #

library(dplyr)
library(ggplot2)
library("ggalluvial")
library("viridis")

ggplot(df, aes(y = Total_Publications, axis1 = Method_Group, axis2 = Topic)) +
  geom_alluvium(aes(fill = Topic, color = after_scale(fill)), 
                width = 1/5, alpha = 1) +
  scale_fill_viridis(discrete=TRUE) +
  geom_stratum(width = 1/5, alpha = 0.2, reverse = TRUE, color = "black") +
  geom_text(stat = "stratum", aes(label = after_stat(stratum)), size= 5, color = "black") +
  scale_x_discrete(limits = c("Ecological Topic", "Ecological Theme"), 
                   expand = c(.05, .05)) +
  theme_minimal() +
  theme(axis.title.y = element_blank(), 
        axis.text.y= element_blank(), 
        legend.position = "none", 
        plot.title = element_text(hjust=0.5, size=18), 
        axis.text.x = element_blank())

修改后的代码（实现需求） #

library(dplyr)
library(ggplot2)
library("ggalluvial")
library("viridis")

ggplot(df, aes(y = Total_Publications, axis1 = Method_Group, axis2 = Topic)) +
  geom_alluvium(aes(fill = Topic, color = after_scale(fill)), 
                width = 1/5, alpha = 1) +
  scale_fill_viridis(discrete=TRUE) +
  # 针对左右两侧轴的分层框设置线宽映射
  geom_stratum(width = 1/5, alpha = 0.2, reverse = TRUE, 
               aes(size = after_stat(axis %in% c(1,2))),
               color = "black") +
  # 自定义线宽值：两侧分层框线宽设为2，其他保持默认1
  scale_size_manual(values = c(`TRUE` = 2, `FALSE` = 1)) +
  geom_text(stat = "stratum", aes(label = after_stat(stratum)), size= 5, color = "black") +
  scale_x_discrete(limits = c("Ecological Topic", "Ecological Theme"), 
                   expand = c(.05, .05)) +
  theme_minimal() +
  theme(axis.title.y = element_blank(), 
        axis.text.y= element_blank(), 
        legend.position = "none", 
        plot.title = element_text(hjust=0.5, size=18), 
        axis.text.x = element_blank())

关键修改点 #

1. 在geom_stratum中，通过after_stat(axis %in% c(1,2))识别左右两侧的轴（axis=1对应左侧，axis=2对应右侧），将线宽与该判断结果绑定
2. 使用scale_size_manual指定线宽：满足条件的分层框（左右两侧）线宽设为2，其余保持默认1（如果有中间轴的话）
3. 该方法仅调整分层框的边框线宽，不会影响geom_alluvium绘制的连接线宽度

内容的提问来源于stack exchange，提问作者Kristen Cyr