geom_bar与geom_errorbar仅单组条形显示误差棒问题排查

你有如下结构的DataFrame：

structure(list(type = c("aerial", "aerial", "aerial", "aerial", 
"TLAcmeth", "TLAcmeth", "TLAcmeth", "TLAcmeth", "TLAmeandaily", 
"TLAmeandaily", "TLAmeandaily", "TLAmeandaily"), season = c("Fall", 
"Spring", "Summer", "Winter", "Fall", "Spring", "Summer", "Winter", 
"Fall", "Spring", "Summer", "Winter"), TotalEffort = c(190673.543181818, 
218904.879166667, 203450.11969697, 56238.5424242424, 268342.820454545, 
285751.855555556, 345593.292424242, 98186.1393939394, 231709.359979371, 
240226.110903571, 297768.291682299, 89965.0324616366), TotalVariance = c(492915253.434218, 
568040077.261171, 647316950.988574, 98882407.0742865, 1809446616.57252, 
1459917672.26073, 2412306298.47967, 249200347.968292, 690088788.630394, 
219887023.857297, 762532238.93411, 184763903.639171), STE = c(22201.6948324721, 
23833.5913630567, 25442.424235685, 9943.96334839819, 42537.5906296128, 
38208.8690261924, 49115.2348918304, 15786.0808299049, 26269.5410814577, 
14828.588060139, 27613.9862919882, 13592.7886630806)), row.names = c(NA, 
-12L), class = "data.frame")

使用这段ggplot代码绘图时：

ggplot(E_StE, aes(x = season, y = TotalEffort, fill = type)) +
  geom_bar(stat = "identity", position = "dodge", color = "black") +
  scale_y_continuous(name = "Estimated Effort (h)", expand = c(0, 0)) +
  geom_errorbar(aes(ymin = TotalEffort-STE, ymax = TotalEffort+STE), position = "dodge", width = 0.2) +
  xlab("Season")

出现的问题是所有误差棒只显示在一组条形上，没有对应到各自的分组条形。

问题出在geom_errorbar的位置设置上：geom_bar默认的position = "dodge"使用的宽度是0.9，但你给geom_errorbar只写了position = "dodge"，没有指定匹配的宽度，导致误差棒的偏移位置和条形不对齐，全部堆到了同一组。

修正方法是把geom_errorbar的位置设置改成position = position_dodge(width = 0.9)，手动指定和条形一致的dodge宽度，这样误差棒就会和对应分组的条形对齐。

修正后的完整代码：

ggplot(E_StE, aes(x = season, y = TotalEffort, fill = type)) +
  geom_bar(stat = "identity", position = position_dodge(width = 0.9), color = "black") +
  scale_y_continuous(name = "Estimated Effort (h)", expand = c(0, 0)) +
  geom_errorbar(aes(ymin = TotalEffort - STE, ymax = TotalEffort + STE), 
                position = position_dodge(width = 0.9), width = 0.2) +
  xlab("Season")

运行这段代码后，每个分组条形都会对应自己的误差棒，不会再出现错位的情况。

内容的提问来源于stack exchange，提问作者Ryan Gary