library(openxlsx)
excel_sample1<-read.xlsx("http://kanggc.iptime.org/book/data/sample1-n.xlsx")
year<-excel_sample1$year
gdp<-excel_sample1$gdp
consumption<-excel_sample1$consumption
lgdp<-log(gdp)
lconsumption<-log(consumption)
lgdp; lconsumption 
names(excel_sample1)
excel_sample1
names(excel_sample1)[3]<-"cons" 
excel_sample1
names(excel_sample1)<-c("T","Y","C") 
excel_sample1