如何更改ggplot2构面的顺序

Question

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, nrow = 3, scales = "free")

和图形如下所示：

一切都很好，直到我注意到变量“ Site”的级别不在我选择的顺序之内。ggplot按字母顺序对其进行排序，如下所示：

pd.long$Site
Levels: BED BEU EB KAD KAU KB KER KOA KOB KOO PNS RO

但是，我希望它们与它们在变量列中出现的顺序相同，即

KOA KOB KOO EB  PNS BED KB  KER KAU KAD RO  BEU

任何帮助将不胜感激。谢谢

Answer 1

重新整理因素

pd.long$Site <- factor(pd.long$Site,levels=c("KOA","KOB","KOO","EB","PNS","BED","KB","KER","KAU","KAD","RO","BEU"))

或更普遍的答案，其中顺序基于Site列中的第一个出现：

pd.long$Site <- factor(pd.long$Site,levels=unique(pd.long$Site))