如何调整ggplot2中小提琴图的X轴显示顺序？

你的核心问题在于：X轴使用的是拼接后的pop_count变量，而非population_ID，所以仅修改population_ID的因子顺序不会直接影响X轴排列。你尝试的方向有道理，但需要调整步骤确保pop_count也遵循指定顺序。

最优解决方案 #

直接基于指定的人群顺序，生成pop_count的因子水平，确保X轴严格按照要求排列：

library(dplyr)
library(readxl)
library(ggplot2)

# 读取数据
variants_dist <- read_excel("path/to/file.xlsm", 10)

# 定义想要的人群顺序
pop_order <- c("AFR", "EUR", "MENA", "SAS", "CEA", "SIB", "OCE", "AME")

# 统计每个人群的样本量，并将population_ID转为指定顺序的因子
df_var <- variants_dist %>%
  mutate(population_ID = factor(population_ID, levels = pop_order)) %>%
  group_by(population_ID) %>%
  summarise(num = n())

# 绘图：生成pop_count并转为对应顺序的因子
variants_dist %>%
  mutate(population_ID = factor(population_ID, levels = pop_order)) %>%
  left_join(df_var) %>%
  mutate(
    # 拼接pop_count，同时基于population_ID的因子顺序生成pop_count的因子水平
    pop_count = paste0(population_ID, "\n", "n=", num),
    pop_count = factor(pop_count, levels = paste0(pop_order, "\n", "n=", df_var$num))
  ) %>%
  ggplot(aes(x = pop_count, y = snps, fill = population_ID)) +
  geom_violin(position = "dodge", trim = FALSE) +
  geom_boxplot(width = 0.07, color = "black", alpha = 0.6) +
  scale_fill_manual(values = c(
    EUR = "dodgerblue2", MENA = "mediumvioletred", SIB = "darkkhaki",
    CEA = "firebrick2", AFR = "olivedrab2", OCE = "powderblue",
    SAS = "darksalmon", AME = "plum2"
  )) +
  theme_bw() +
  theme(legend.position = "none") +
  xlab("")

对你尝试方法的说明 #

你之前的步骤：

variants_dist <- variants_dist %>%
  mutate(population_ID=factor(population_ID, levels=c("AFR", "EUR", "MENA", "SAS", "CEA", "SIB", "OCE", "AME")))
variants_dist %>% arrange(population_ID) -> pop_sort

这一步是对的，但后续用forcats::fct_inorder(pop_count)时，需要确保pop_count在排列后的数据集里是按组唯一出现的（即每个组的pop_count只出现一次在排序后的开头），这种方法也能生效，但不如直接指定pop_count的因子水平稳妥——如果数据排列时出现组内重复的pop_count，fct_inorder可能会出现错误的顺序。

关键逻辑 #

• 先将population_ID转为指定顺序的因子，确保分组统计时的顺序正确
• 生成pop_count的因子水平时，直接复用预先定义的人群顺序，结合统计出的样本量，严格对应目标排列

内容的提问来源于stack exchange，提问作者Matteo