resppszse2<-ur.pp(Dstocks$SZSE,type="Z-tau",model="trend",lags="short")
resppsci2<-ur.pp(Dstocks$SCI,type="Z-tau",model="trend",lags="short")
resppgei2<-ur.pp(Dstocks$GEI,type="Z-tau",model="trend",lags="short")
在运行以上程序的时候出现了如下的问题
> resppszse2<-ur.pp(Dstocks$SZSE,type="Z-tau",model="trend",lags="short")
Error in Dstocks$SZSE : $ operator is invalid for atomic vectors
> resppsci2<-ur.pp(Dstocks$SCI,type="Z-tau",model="trend",lags="short")
Error in Dstocks$SCI : $ operator is invalid for atomic vectors
> resppgei2<-ur.pp(Dstocks$GEI,type="Z-tau",model="trend",lags="short")
Error in Dstocks$GEI : $ operator is invalid for atomic vectors
> summary(resppszse2)

请问大神这个该怎么解决？