如何用R的ggplot2绘制X轴两侧分属正负Y轴的柱状图

要实现ER在Y轴正区间向上展示、GEP在Y轴负区间向下展示的合并双向柱状图，直接在同一个ggplot对象中叠加两组图层即可，核心是将GEP的Y值取负映射，对应代码如下：

library(ggplot2)

combined.2015.bar <- ggplot(Salix_data.2015, aes(x = Flux_Date, fill = Treatment)) +
  # 叠加ER正向图层
  stat_summary(aes(y = ER), fun=mean, geom="bar", position="dodge", width =0.8, alpha = 0.8) +
  stat_summary(aes(y = ER), fun.data = mean_se, geom = "errorbar",
               width=0.2, position = position_dodge(0.8)) +
  # 叠加GEP负向图层，y取负实现向下展示
  stat_summary(aes(y = -GEP), fun=mean, geom="bar", position="dodge", width =0.8, alpha = 0.5) +
  stat_summary(aes(y = -GEP), fun.data = mean_se, geom = "errorbar",
               width=0.2, position = position_dodge(0.8)) +
  # ER显著性标注，和原有逻辑一致
  annotate(geom = "text", x = 1, y = 8000, label = "a")+
  annotate(geom = "text", x = 2, y = 5000, label = "a")+
  annotate(geom = "text", x = 3, y = 7500, label = "b")+
  annotate(geom = "text", x = 3, y = 8000, label = "*")+
  annotate(geom = "text", x = 4, y = 3000, label = "a")+
  # GEP显著性标注，y保持负向即可
  annotate(geom = "text", x = 1, y = -20000, label = "a")+
  annotate(geom = "text", x = 2, y = -12000, label = "b")+
  annotate(geom = "text", x = 3, y = -17000, label = "a")+
  annotate(geom = "text", x = 4, y = -10000, label = "a")+
  annotate(geom = "text", x = 3, y = -19000, label = "*")+
  # Y轴标签转换，负区间显示GEP绝对值避免阅读混淆
  scale_y_continuous(labels = function(x) ifelse(x<0, -x, x),
                     name = "ER / GEP") +
  # 主题与标题设置
  theme(legend.position = "bottom") +
  labs(title = "2015年北极柳灌丛ER与GEP按日期和处理分组对比", x="日期")

print(combined.2015.bar)

可调整细节 #

• 代码中用alpha透明度区分两类指标的柱子，你也可以取消alpha参数，或者修改fill映射规则为fill = interaction(Treatment, 指标类型)，用不同色系直接区分ER和GEP
• 如需分别设置两个指标的Y轴标签，可添加次轴配置：scale_y_continuous(..., sec.axis = sec_axis(~.*-1, name = "GEP"))，主Y轴对应ER，次Y轴对应GEP

内容的提问来源于stack exchange，提问作者user16900506