[R] Trouble with [sv]apply

[Worik R]

Friends

I clearly donot understand how sapply and vapply work.

What I have is a function that returns a matrix with an indeterminate
number of rows (some times zero) but a constant number of columns.  I
cannot reliably use an apply function to assemble the matrices into a
matrix.  I am not sure it is possible.

I can demonstrate the core of my confusion with this simple code.

A.f <- function(i){
  ret <- matrix("a", i, 7)
  cat(i, class(ret), dim(ret), "\n")
  return(ret)
}
V.f <- function(){
  SS <- vapply(c(1,2),
                 A.f,
                 rep('a', 7))
  return(SS)
}
S.f <- function(){
  SS <- sapply(c(1,2),
                 A.f)
  cat("SS", class(SS), dim(SS), "\n")
  return(SS)
}


Calling V.f() fails:

> V.f()
1 matrix 1 7
2 matrix 2 7
Error in vapply(c(1, 2), A.f, rep("a", 7)) :
  values must be length 7,
 but FUN(X[[2]]) result is length 14
>


Calling S.f() returns a list.


Do I have to accept I am going to be getting a list and I have to
assemble a matrix in a loop?

cheers
Worik