我有一个类似于以下内容的分类数据集:
A<-data.frame(animal=c("cat","cat","cat","dog","dog","dog","elephant","elephant","elephant"),
color =c(rep(c("blue","red","green"),3)))
我想订购它,以便动物用狗,然后大象,然后猫,然后颜色分为绿色,蓝色,然后红色.所以最后它看起来像
狗绿色,狗蓝色,狗红色,大象绿色,大象蓝色,...