如何用ggplot2的facet_grid绘制office列所有离散值组合的散点图？

需求说明 #

现有包含district（选区）、office（职位）、margin（得票差）的数据集，需要绘制所有职位两两组合的散点图网格，让每个职位同时作为行和列的分面变量，形成完整的4×4散点图矩阵。

数据集 #

library(tidyverse)

df <- structure(list(district = c(1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 
3), office = c("GOV", "WAG", "USS", "WST", "GOV", "WAG", "USS", 
"WST", "GOV", "WAG", "USS", "WST"), margin = c(-10.6296758104738, 
-11.0540006895039, -16.2188249213812, -15.4710156423517, -12.7093173035638, 
-12.9545865749955, -17.3703863277323, -17.4593332847035, -10.1910380671443, 
-10.984606653898, -14.8799042051138, -15.8511248029804)), row.names = c(NA, 
-12L), class = c("tbl_df", "tbl", "data.frame"))

解决方案 #

无需用patchwork拼接，只需先重构数据结构，再用facet_grid一步实现：

方法1：简洁重塑版

# 将数据转宽格式，每个职位的得票差单独成列
df_wide <- df %>% 
  pivot_wider(names_from = office, values_from = margin)

# 构造y轴职位的长格式数据，再交叉所有x轴职位
plot_data <- df_wide %>%
  pivot_longer(cols = GOV:WST, names_to = "y_office", values_to = "y_value") %>%
  crossing(x_office = unique(df$office)) %>%
  mutate(x_value = pull(df_wide, x_office))

# 绘制全组合网格散点图
ggplot(plot_data, aes(x = x_value, y = y_value)) +
  geom_point() +
  facet_grid(y_office ~ x_office) +
  scale_x_continuous(limits = range(df$margin)) +
  scale_y_continuous(limits = range(df$margin)) +
  theme_bw()

方法2：显式映射版（适合新手理解）

# 转宽格式
df_wide <- df %>% 
  pivot_wider(names_from = office, values_from = margin)

# 构造所有行/列职位组合，并映射对应数值
plot_data <- df_wide %>%
  crossing(y_office = unique(df$office), x_office = unique(df$office)) %>%
  mutate(
    y_value = case_when(
      y_office == "GOV" ~ GOV,
      y_office == "WAG" ~ WAG,
      y_office == "USS" ~ USS,
      y_office == "WST" ~ WST
    ),
    x_value = case_when(
      x_office == "GOV" ~ GOV,
      x_office == "WAG" ~ WAG,
      x_office == "USS" ~ USS,
      x_office == "WST" ~ WST
    )
  )

# 绘图
ggplot(plot_data, aes(x = x_value, y = y_value)) +
  geom_point() +
  facet_grid(y_office ~ x_office) +
  scale_x_continuous(limits = range(df$margin)) +
  scale_y_continuous(limits = range(df$margin)) +
  theme_bw()

效果说明 #

最终会生成4行（对应y轴的4个职位）×4列（对应x轴的4个职位）的散点图网格，每个子图展示对应职位对的得票差关联关系。统一设置轴范围后，所有子图刻度一致，便于跨组对比。

内容的提问来源于stack exchange，提问作者John J.