使用ggalluvial绘制物种组成变化桑基图报错求助

报错原因 #

你的代码报错核心是数据格式不符合ggalluvial的要求：

• alluvium参数应映射到连接不同x轴类别的分组变量（此处为物种acc），而非数值sum_n
• 最后一步group_by(scenario, acc) %>% summarise()丢失了物种在两个场景间的对应关系，导致工具无法识别为冲积图格式

修正后的完整代码 #

以下代码可正确生成符合预期的桑基图：

library(ggalluvial)
library(tidyverse)

# 测试数据初始化
df_test <- data.frame(site = c(1,1,1,2,2,1,2,2,2,2),
                      site_ch = c("a","a","a","b","b","a","b","b","b","b"),
                      acc = c("piab", "abies", "fasy", "piab", "fasy",
                              "frax", "piab", "fasy", "frax", "abies"),
                      scenario = rep(c("current", 'rcp25'), each = 5)) %>% 
  mutate(acc = factor(acc),
         site_ch = factor(site_ch),
         scenario = factor(scenario))

# 数据预处理：确保每个物种在两个场景下都有记录
df_alluvial <- df_test %>%
  # 按站点、场景、物种统计出现频次
  count(site, scenario, acc, name = "freq") %>%
  # 补全所有物种-场景-站点组合，缺失的频次填0
  complete(site, scenario, acc, fill = list(freq = 0)) %>%
  # 按物种和场景汇总总频次
  group_by(scenario, acc) %>%
  summarise(total_freq = sum(freq, na.rm = TRUE), .groups = "drop") %>%
  # 固定场景顺序，保证current在前、rcp25在后
  mutate(scenario = factor(scenario, levels = c("current", "rcp25")))

# 绘制桑基图
ggplot(df_alluvial,
       aes(x = scenario, 
           stratum = acc, 
           alluvium = acc,  # 关键：用物种作为连接不同场景的分组变量
           y = total_freq, 
           fill = acc)) +
  geom_alluvium(alpha = 0.6) +  # 绘制物种跨场景的连接流
  geom_stratum(color = "white") +  # 绘制分层块，添加白色边框提升可读性
  geom_text(stat = "stratum", aes(label = acc)) +  # 在分层块上标注物种名称
  theme_minimal() +
  labs(title = "物种组成跨气候变化场景变化",
       x = "场景",
       y = "总出现频次",
       fill = "物种") +
  scale_fill_brewer(palette = "Set2")

关键调整说明 #

1. 修正alluvium映射：将alluvium = sum_n改为alluvium = acc，让ggalluvial识别到是同一个物种在不同场景间的流动
2. 保留物种对应关系：通过complete()补全所有物种-场景组合，确保每个物种在两个场景下都有数据行（哪怕频次为0）
3. 优化可视化细节：添加物种名称标签、分层块边框，提升图表可读性

扩展：按站点分组展示 #

如果需要同时展示不同站点的物种变化，可保留站点信息并添加分面：

# 保留站点维度的版本
df_alluvial_site <- df_test %>%
  count(site, scenario, acc, name = "freq") %>%
  complete(site, scenario, acc, fill = list(freq = 0)) %>%
  mutate(scenario = factor(scenario, levels = c("current", "rcp25")),
         site = paste("站点", site))

ggplot(df_alluvial_site,
       aes(x = scenario, 
           stratum = acc, 
           alluvium = acc, 
           y = freq, 
           fill = acc)) +
  geom_alluvium(alpha = 0.6) +
  geom_stratum(color = "white") +
  geom_text(stat = "stratum", aes(label = acc), size = 3) +
  facet_wrap(~site) +  # 按站点分面展示
  theme_minimal() +
  labs(title = "各站点物种组成跨气候变化场景变化",
       x = "场景",
       y = "出现频次",
       fill = "物种") +
  scale_fill_brewer(palette = "Set2")

内容的提问来源于stack exchange，提问作者maycca