map<-rep(c("A","B","C","D"),8)

matrix(sample(map),nrow=4)

matrix(sample(map),nrow=4)

matrix(rep(1:8,rep(4,8)),nrow=4)

trt<-c("A","B","C","D")
r<-NULL
for (i in 1:8) r<-c(r,sample(trt))

matrix(r,nrow=4)

sample(trt)

sample(trt[trt!="C"])

sample(trt[trt!="B"& trt!="D"])

sample(trt[trt != "A" &  trt != "D"])

sample(trt[trt!="C"& trt!="D"])

sample(trt[trt!="A"& trt!="B"])



