Double for loop in R

Question

I want to create a data set using the following code, the aim is to add a blank row between each group, and three blank rows between each treatment. I wish it looks as the following dataset.

value group treatment
 39.7     A         1
 53.5     A         1
 51.1     A         1
 67.8     A         1

 84.8     B         1
 80.3     B         1
 79.6     B         1
 84.3     B         1



 31.0     C         2
 32.0     C         2
 33.0     C         2
 34.0     C         2

  1.0     D         2
  2.0     D         2
  3.0     D         2
  4.0     D         2

I wrote down a double for loop but it doesn't work well. I can't figure it out. Can anyone tell me what is the problem with it?

mydata <- data.frame(value=c(39.7,53.5,51.1,67.8,84.8,80.3,79.6,84.3,31,32,33,34,1,2,3,4),group=c("A","A","A","A","B","B","B","B","C","C","C","C","D","D","D","D"),treatment=c(1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2))

blank <- data.frame(value=NA,group="NA",treatment=NA)
blank1 <- data.frame(value=c(NA,NA,NA),group=c("NA","NA","NA"),treatment=c(NA,NA,NA))

uni<-unique(mydata$treatment)
b<-length(uni)
out <- c()
out1<-c()

for (i in 1:b) {
  emp<-subset(mydata,treatment==uni[i])
  uni1<-unique(emp$group)
  c<-length(uni1)
  for (j in 1:c){
    emp1<-subset(subset(mydata,treatment==uni[i]),group==uni1[j])
    stack<-rbind(emp1,blank)
    out<-rbind(stack,out)
  }
  stack1<-rbind(out,blank1)
  out1<-rbind(stack1,out1)
}

Answer 1

I can't imagine a practical reason for having data with blank rows in such a pattern, so I'm assuming it is simply for printing:

printables <- lapply(
  split(mydata,mydata$treatment),
  function(t)
    split(t,as.character(t$group)))

for (t in seq_along(printables)){
  for(g in seq_along(printables[[t]])){
    print(printables[[t]][[g]],row.names=FALSE)
    cat('\n')
  }
  cat('\n\n')
}