如何在ggplot中按特定处理（如VIP）的升序排列箱线图

希望将箱线图按照特定处理（例如VIP）的数值升序排列，目前X轴的Code是按字母顺序展示的，请问如何修改代码实现这个需求？

示例数据集 #

Peso <- structure(list(Accession = c("Potato", "Potato", "Potato", "Potato", 
"Potato", "Potato"), Genotype = c("#1", "#2", "#3", "#4", "#5", 
"#6"), Code = c("aa", "ab", "ac", "ad", "ae", "af"), Nome = c("L", 
"L", "L", "L", "L", "L"), Data = c("A", "A", "A", "A", "A", "A"
), Treatment = c("VIP", "VIP", "VIP", "MOCK", "MOCK", "MOCK"), 
    Weight = c(1.9, 1.46, 1.52, 1.29, 1.05, 1.52)), class = c("tbl_df", 
"tbl", "data.frame"), row.names = c(NA, -6L))

现有绘图代码 #

Population <- ggplot(data = na.omit(Peso), aes(x = Code, y = Weight, fill = Treatment)) + 
  geom_boxplot( alpha=0.2) + 
  xlab("Genotype") + 
  geom_point()+
  ylim(0, 3.00)

Population + ggtitle("21dpi Dry-Weight") +
  ylab("Weight (g)") +
  xlab("Genotype") +
  theme(plot.title = element_text(family = NULL, face = NULL, color = "black", size = 15)) +
  theme(axis.title.x = element_text(family = NULL, face = NULL, color = "black", 14)) +
  theme(axis.title.y = element_text(family = NULL, face = NULL, color = "black", 14)) +
  theme(axis.text.x = element_text(angle = 90, vjust = 0.5, hjust = 1, size = 9)) + 
  scale_fill_manual(values=c("#33FF00", "#000000"))

核心思路是将Code转换为有序因子，排序依据为VIP处理组内该Code对应的Weight统计值（均值/中位数均可），具体步骤如下：

1. 提取VIP组数据，计算每个Code的Weight均值（或中位数）并排序
2. 将原数据中的Code转换为按上述顺序排列的因子
3. 基于转换后的因子绘图

修改后的完整代码：

library(dplyr)
library(ggplot2)

# 1. 生成VIP组Weight均值升序的Code顺序
vip_sorted_codes <- Peso %>%
  filter(Treatment == "VIP") %>%
  group_by(Code) %>%
  summarise(avg_weight = mean(Weight)) %>%
  arrange(avg_weight) %>%
  pull(Code)

# 2. 将Code转为有序因子，指定排序规则
Peso$Code <- factor(Peso$Code, levels = vip_sorted_codes, ordered = TRUE)

# 3. 绘制箱线图（X轴自动按因子顺序排列）
Population <- ggplot(data = na.omit(Peso), aes(x = Code, y = Weight, fill = Treatment)) + 
  geom_boxplot(alpha=0.2) + 
  xlab("Genotype") + 
  geom_point()+
  ylim(0, 3.00)

Population + ggtitle("21dpi Dry-Weight") +
  ylab("Weight (g)") +
  xlab("Genotype") +
  theme(plot.title = element_text(family = NULL, face = NULL, color = "black", size = 15)) +
  theme(axis.title.x = element_text(family = NULL, face = NULL, color = "black", size = 14)) +
  theme(axis.title.y = element_text(family = NULL, face = NULL, color = "black", size = 14)) +
  theme(axis.text.x = element_text(angle = 90, vjust = 0.5, hjust = 1, size = 9)) + 
  scale_fill_manual(values=c("#33FF00", "#000000"))

补充说明 #

• 若需要用中位数排序，只需把summarise(avg_weight = mean(Weight))替换为summarise(med_weight = median(Weight))即可
• 因子转换后，ggplot会自动遵循指定的levels顺序绘制X轴，不再使用默认的字母排序

内容的提问来源于stack exchange，提问作者Luigi