### CONVERT THE FACTOR TO DUMMIES ###

library(caret)

dummies <- predict(dummyVars(~ Species, data = iris), newdata = iris)

head(dummies, n = 3)

### CONVERT DUMMIES TO THE FACTOR ###

header <- unlist(strsplit(colnames(dummies), '[.]'))[2 * (1:ncol(dummies))]

species <- factor(dummies %*% 1:ncol(dummies), labels = header)

str(species)

#顺便提示一下，rda或cca函数，如果用公式模型（就是表达式带有～）已经自动将分类变量变为哑变量（0-1数据）