recursively split list elements

Question

I cannot find the right incantation of Reduce, Recall, lapply to perform the following task. Consider the following function,

bisect.df <- function(d){
  n <- ncol(d)
  if(n%%2) n <- n-1 # drop one col if odd number
  ind <- sample(n)[seq.int(n/2)] # split randomly both parts

  list(first=d[, ind],
       second=d[, -ind])
}

given a data.frame, it returns a list of two children data.frames of equal ncol extracted randomly from their parent. I wish to apply this function recursively to the offsprings down to a given level, say 3 generations. I can do it trivially one generation at a time,

bisect.list <- function(l){
  unlist(lapply(l, bisect.df), recursive=FALSE)
}

but how do I call this recursively, say N=3 times?

Here's a test sample to play with

d <- data.frame(matrix(rnorm(16*5), ncol=16))
step1 <- bisect.list(list(d))
step2 <- bisect.list(step1)
step3 <- bisect.list(step2)
str(list(step1, step2, step3))

Answer 1

bisect.list <- function(l,n){
  for(i in 1:n) {
    l <- unlist(lapply(l, bisect.df), recursive=FALSE)
  }
  return(l)
}

not sure how to do it without a loop...