如何在一个箱形图中获得两个X轴

Question

I'm trying to get two x-axes in a boxplot in ggplot2; one is Site and the other is Region. I have 11 different Sites and 3 Regions, and want to display my data such that Region is below Site, encompassing a few sites each.

I've tried facet wrapping and gridding, but I want only one graph where all observations are displayed.

My data looks somewhat like this:

Region   Site     Value
South   Site1       0.1
South   Site1       0.3
South   Site2      0.24
South   Site2      0.03
South   Site3      0.06
South   Site3      0.14
South   Site3      0.02
Central Site4       0.4
Central Site4      0.32
Central Site4      0.45
Central Site5      0.22
Central Site5      0.27
Central Site5      0.13
Central Site6      0.09
North   Site7      0.55
North   Site7      0.34
North   Site8      0.67
North   Site9      0.89 
North   Site9       0.7
North   Site9      0.51

The relevant code looks somewhat like this:

graph <- ggplot(dataframe, aes(x=Site, y=Value)) + geom_boxplot()

I'm hoping to get one graph where the Sites are represented by their associated Regions, ideally with each region label only showing up once under the set of the Sites each represents.

Answer 1

Use ordered factors to groups levels in variables. I used y-axes because the Region levels are cardinal.

Best, Tyler

library(tidyverse)

dat <- tribble(
  ~Region,   ~Site,   ~Value,
  "South",   "Site1",    0.1,
  "South",   "Site1",    0.3,
  "South",   "Site2",   0.24,
  "South",   "Site2",   0.03,
  "South",   "Site3",   0.06,
  "South",   "Site3",   0.14,
  "South",   "Site3",   0.02,
  "Central", "Site4",    0.4,
  "Central", "Site4",   0.32,
  "Central", "Site4",   0.45,
  "Central", "Site5",   0.22,
  "Central", "Site5",   0.27,
  "Central", "Site5",   0.13,
  "Central", "Site6",   0.09,
  "North",   "Site7",   0.55,
  "North",   "Site7",   0.34,
  "North",   "Site8",   0.67,
  "North",   "Site9",   0.89, 
  "North",   "Site9",    0.7,
  "North",   "Site9",   0.51)

dat <- 
  dat %>% 
  mutate(
    Region = factor(x = Region, levels = c("South", "Central", "North"), ordered = T), 
    Site = factor(x = Site) %>% fct_rev())

ggplot(data = dat, mapping = aes(x = Region, y = Value, position = fct_rev(Site), fill = Site)) + 
  geom_boxplot() + 
  coord_flip()