x1<-runif(200,0,1);
x2<-runif(1000,5,6);
x3<-runif(1000,10,12);
x<-c(x1,x2,x3);
##Simple random sampling
means1<-matrix(0,1,100);
for(i in 1:100)
{
xsamp<-sample(x,220);
means1[i]<-mean(xsamp);
}
sd1<-sd(means1[1,]); m1<-mean(means1[1,]);
cat("Mean by simple sampling is",m1, "and SD is",sd1,"\n");
##Stratified sampling
means2<-matrix(0,1,100);
for(i in 1:100)
{
xsample1<-sample(x1,20);
xsample2<-sample(x2,100);
xsample3<-sample(x3,100);
means2[i]<-mean(xsample1)*20/220 + mean(xsample2)*100/220 + mean(xsample3)*100/220;
}
sd2<-sd(means2[1,]); m2<-mean(means2[1,]);
cat("Mean by stratified sampling is",m2, "and SD is",sd2,"\n");
##postscript("strat.eps");
par(mfrow=c(1,2));
hist(means1[1,], xlab="",main="Simple random sampling", cex.lab=1.5,cex.axis=1.5, font.axis=2, font.lab=2);
hist(means2[1,], xlab="",ylab="", main="Stratified sampling", cex.lab=1.5,cex.axis=1.5, font.axis=2, font.lab=2);
##dev.off();