基于单个DataFrame绘制并列双条形图的格式问题

问题详情 #

想让两组条形并列显示而非堆叠，但用position_dodge实现失败。使用的DataFrame（combinedCountFrame）如下：

system n.x n.y
1            T-64BV   7  65
2             T-72A   8   0
3            T-72AV   3   2
4             T-72B  47   2
5   T-72B Obr. 1989  13   0
6            T-72B3  30   0
7  T-72B3 Obr. 2016  70   0
8            T-80BV  11   3
9           T-80BVM  18   0
10            T-80U  44   0
11           T-80UK   2   0
12          T-80UM2   1   0
13            T-90A  17   0
14     Unknown tank  25   1
15          T-64B1M   0   1
16          T-72AMT   0   3

绘图代码：

ggplot(combinedCountFrame, aes(x = system)) +
    geom_bar(aes(y = n.x, fill = "Russia"), stat = "identity", position = position_dodge(width = 0.8)) +
    geom_bar(aes(y = n.y, fill = "Ukraine"), stat = "identity", position = position_dodge(width = 0.8)) +
    labs(
      title = paste(equipmentType, "Losses", sep = " "),
      y = "# of Systems Lost",
      fill = "Country"
    ) +
    theme_minimal() +
    theme(
      legend.position = "top",
      axis.text.x = element_text(angle = 45, hjust = 1)
    )

生成的图表中条形是堆叠状态，没有实现并列。

解决方法 #

问题根源在于你的数据是宽格式，而ggplot绘制分组条形图需要长格式数据。先转格式再绘图即可解决：

1. 转换数据格式 #

用tidyr包的pivot_longer把宽表转成长表：

library(tidyr)
library(dplyr)

long_df <- combinedCountFrame %>%
  pivot_longer(
    cols = c(n.x, n.y),
    names_to = "Country",
    values_to = "Losses",
    names_prefix = "n."
  ) %>%
  mutate(Country = ifelse(Country == "x", "Russia", "Ukraine"))

2. 绘制并列条形图 #

用转换后的长数据绘图，只需要一组geom_bar，并在aes里指定fill = Country，配合position_dodge：

ggplot(long_df, aes(x = system, y = Losses, fill = Country)) +
  geom_bar(stat = "identity", position = position_dodge(width = 0.8), width = 0.7) +
  labs(
    title = paste(equipmentType, "Losses", sep = " "),
    y = "# of Systems Lost",
    fill = "Country"
  ) +
  theme_minimal() +
  theme(
    legend.position = "top",
    axis.text.x = element_text(angle = 45, hjust = 1)
  )

关键说明 #

• 宽转长是ggplot处理分组图的标准流程，这样ggplot能明确每个分组对应的数值，自动处理并列逻辑。
• position_dodge(width = 0.8)控制两组条形的间距，width = 0.7控制单条条形的宽度，可根据视觉效果调整。

内容的提问来源于stack exchange，提问作者Scipio