sample1<-"http://kanggc.iptime.org/book/data/sample1.txt" 
sample_dat<- as.matrix(read.delim(sample1,header=T),ncol=3)
sample_dat
year<-sample_dat[,1]
year
gdp<-sample_dat[,2]
gdp
consumption<-sample_dat[,3]
consumption
colMeans(sample_dat)
summary(sample_dat)