我有一个具有以下结构的数据帧“ pd.long”：
> str(pd.long)
'data.frame': 144 obs. of 3 variables:
$ Site : Factor w/ 12 levels "BED","BEU","EB",..: 8 9 10 3 11 1 6 7 5 4 ...
$ Month : Factor w/ 12 levels "Dec","Jan","Feb",..: 1 1 1 1 1 1 1 1 1 1 ...
$ Density: int 20 20 20 20 20 20 20 20 20 20 ...
我用这段代码构建了条形图：
ggplot(pd.long, aes(x=Month, y=Density, fill=Site))+
geom_bar(stat = "identity", position = "dodge", fill = "darkgray")+
xlab("Month") + ylab("Number")+
facet_wrap(~Site, …