library(openxlsx)
sample1<-read.xlsx("http://kanggc.iptime.org/book/data/sample1-n.xlsx")

year<-sample1$year
gdp<-sample1$gdp
consumption<-sample1$consumption

lgdp<-log(gdp)
lconsumption<-log(consumption)

lgdp
lconsumption 

names(sample1)
sample1

names(sample1)[3]<-"cons" 
sample1

names(sample1)<-c("T","Y","C") 
sample1