语言是这样的
write.table(presidential,'presidential.csv',row.names=F,sep=",")
write.table(presidential,'presidential.txt',row.names=F,sep=",")
presidential.csv<-read.csv("presidential.csv",header=T,stringsAsFactors=F,sep=",")
presidential.csv
presidential
presidential.csv<-as.Date(presidential.csv$start,"%y/%m/%d")
presidential.csv<-as.Date(presidential.csv$end,"%y/%m/%d")
identical(presidential.csv,presidential)

最后想要检验presidential.csv和presidential是否一样。其中
presidential.csv<-as.Date(presidential.csv$end,"%y/%m/%d")总是报错“$ operator is invalid for atomic vectors”，不知道是否有办法解决。如果解决了这个问题，是否最后的idetical能得到T的答案？..
谢谢了！！