ggplot使用geom_split_violin绘制按性别拆分的单分组小提琴图

不需要修改你现有geom_split_violin的自定义函数代码，仅需调整ggplot的映射参数即可实现：

• 核心逻辑：原函数通过分组的group序号奇偶性决定左右摆放位置，单分组场景下将x映射为固定值（无需多分类x变量）即可让两个性别分组的小提琴在同一个x轴位置拆分展示。

完整示例代码 #

首先保留你现有的自定义函数代码：

GeomSplitViolin <- ggproto("GeomSplitViolin", GeomViolin, 
                           draw_group = function(self, data, ..., draw_quantiles = NULL) {
  data <- transform(data, xminv = x - violinwidth * (x - xmin), xmaxv = x + violinwidth * (xmax - x))
  grp <- data[1, "group"]
  newdata <- plyr::arrange(transform(data, x = if (grp %% 2 == 1) xminv else xmaxv), if (grp %% 2 == 1) y else -y)
  newdata <- rbind(newdata[1, ], newdata, newdata[nrow(newdata), ], newdata[1, ])
  newdata[c(1, nrow(newdata) - 1, nrow(newdata)), "x"] <- round(newdata[1, "x"])

  if (length(draw_quantiles) > 0 & !scales::zero_range(range(data$y))) {
    stopifnot(all(draw_quantiles >= 0), all(draw_quantiles <=
      1))
    quantiles <- ggplot2:::create_quantile_segment_frame(data, draw_quantiles)
    aesthetics <- data[rep(1, nrow(quantiles)), setdiff(names(data), c("x", "y")), drop = FALSE]
    aesthetics$alpha <- rep(1, nrow(quantiles))
    both <- cbind(quantiles, aesthetics)
    quantile_grob <- GeomPath$draw_panel(both, ...)
    ggplot2:::ggname("geom_split_violin", grid::grobTree(GeomPolygon$draw_panel(newdata, ...), quantile_grob))
  }
  else {
    ggplot2:::ggname("geom_split_violin", GeomPolygon$draw_panel(newdata, ...))
  }
})

geom_split_violin <- function(mapping = NULL, data = NULL, stat = "ydensity", position = "identity", ..., 
                              draw_quantiles = NULL, trim = TRUE, scale = "area", na.rm = FALSE, 
                              show.legend = NA, inherit.aes = TRUE) {
  layer(data = data, mapping = mapping, stat = stat, geom = GeomSplitViolin, 
        position = position, show.legend = show.legend, inherit.aes = inherit.aes, 
        params = list(trim = trim, scale = scale, draw_quantiles = draw_quantiles, na.rm = na.rm, ...))
}

然后构造示例数据+绘图：

# 构造示例数据：仅包含性别和测量值两个字段
my_data <- data.frame(
  性别 = sample(c("男", "女"), 1000, replace = TRUE)
)
my_data$测量值 <- rnorm(1000, mean = c(0, 1.2)[as.factor(my_data$性别)])

# 单分组拆分小提琴图绘制
ggplot(my_data, aes(x = "总样本", y = 测量值, fill = 性别)) + 
  geom_split_violin(trim = FALSE) +
  # 可选优化：去掉x轴无用标签，调整主题
  labs(x = NULL) +
  theme_classic()

如果需要展示分位数线，直接加draw_quantiles参数即可，比如展示中位数：

ggplot(my_data, aes(x = "总样本", y = 测量值, fill = 性别)) + 
  geom_split_violin(trim = FALSE, draw_quantiles = 0.5) +
  labs(x = NULL) +
  theme_classic()

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