#Schemat losowania zaproponowanz przez Rao-Sampforda.
#liczebnosc proby :
n<-2
x<-c(2, 5, 4, 6, 7, 11, 8, 9, 3, 5)
los_Rao_Sampford<-function(n,x){
x<-as.matrix(x)
N<-nrow(x)
p<-matrix(0,N, 1)
q<-matrix(0,N, 1)
s<-matrix(0, n, 1)
sor<-matrix(0, n, 1)
xx<-sum(x); 
p<-n * x/xx
for(i in 1:N)q[i] <-p[i]/(1-p[i])
a<-1/sum(q); q <-a * q
lp<-0; id <-1
while(id == 1){
id<-0;
s<-sample(1:N,n,replace=TRUE,q)
sor<-sort(s)
i<-1
while((id==0)&(i<n)){
if (sor[i+1]==sor[i]) id<-1
i<-i + 1}}
s}

los_Rao_Sampford(n,x)