目的：为展示不同数据分布的差异。

1. ggplot2 实现

# 准备数据
dat=mtcars[, c("mpg", "cyl")]
colnames(dat)=c("value", "type")
head(dat)
#                  value type
#Mazda RX4         21.0   6
#Mazda RX4 Wag     21.0   6
#Datsun 710        22.8   4

cols=c("#F71480", "#76069A", "#FF8000")
#
p1=ggplot(dat, aes(x = value, fill = as.factor(type) ) ) +
  geom_density(alpha = 0.8) +
  scale_fill_manual(values = cols)+
  facet_wrap(~type, ncol=1) +  # 按气缸数分面
  labs(title = "Density of MPG by Cylinder Count-A",
       x = "Miles Per Gallon (MPG)",
       y = "Density",
       fill = "Cylinders") +
  theme_classic(base_size = 14)+
  theme(strip.background = element_blank(),  # 去掉小标题背景
        strip.placement = "outside");p1  # 小标题外部显示
#
p2=ggplot(dat, aes(x = value, fill = as.factor(type) ) ) +
  geom_density(alpha = 0.8) +
  scale_fill_manual(values = cols)+
  facet_wrap(~type, ncol=1, scales="free_y") +  # 按气缸数分面
  labs(title = "Density of MPG by Cylinder Count-B",
       x = "Miles Per Gallon (MPG)",
       y = "Density",
       fill = "Cylinders") +
  theme_classic(base_size = 14)+
  theme(strip.background = element_blank(),  # 去掉小标题背景
        strip.placement = "outside"); p2  # 小标题外部显示
#

2. 使用R包 ggridges

图放这里，方便和上图类似。

library(ggridges)
pB=ggplot(dat, aes(x = value, y = type, fill = factor(type, levels = c("4", "6", "8")) )) + 
  ggridges::geom_density_ridges(alpha = 0.7, show.legend = T) +
  scale_fill_manual(values = cols)+
  #scale_y_continuous( expand = c(0,0) )+
  labs(title = "Density of MPG by Cylinder Count-C",
       x = "Miles Per Gallon (MPG)",
       y = "Density",
       fill = "Cylinders") +
  theme_classic(base_size = 14); pB
#
pB2=ggplot(dat, aes(x = value, y = type, fill = factor(type, levels = c("4", "6", "8")) )) + 
  ggridges::geom_density_ridges(alpha = 0.7, show.legend = T, 
                                stat="binline", bins=25) +
  scale_fill_manual(values = cols)+
  #scale_y_continuous( expand = c(0,0) )+
  labs(title = "Density of MPG by Cylinder Count-D",
       x = "Miles Per Gallon (MPG)",
       y = "Density",
       fill = "Cylinders") +
  theme_classic(base_size = 14); pB2
#

3. 去掉底部的空隙

pB3=ggplot(dat, aes(x = value, y = type, fill = factor(type, levels = c("4", "6", "8")) )) + 
  ggridges::geom_density_ridges(alpha = 0.7, show.legend = T, 
                                scale = 2) +
  scale_fill_manual(values = cols)+
  #scale_y_continuous( expand = c(0,0) )+
  labs(title = "Density of MPG by Cylinder Count-E\nset scale=2",
       x = "Miles Per Gallon (MPG)",
       y = "Density",
       fill = "Cylinders") +
  # 去掉底部
  scale_y_discrete(expand = c(0, 0)) +     # will generally have to set the `expand` option
  scale_x_continuous(expand = c(0, 0)) +   # for both axes to remove unneeded padding
  coord_cartesian(clip = "on") + # to avoid clipping of the very top of the top ridgeline
  theme_classic(base_size = 14); pB3

Ref

• https://zhuanlan.zhihu.com/p/560080959
• https://wilkelab.org/ggridges/
• https://cran.r-project.org/web/packages/ggridges/vignettes/introduction.html