[R] flatten a list of lists

[Michael Friendly]

I have functions that generate lists objects of class "foo" and lists of 
lists of these, of class
"foolist", similar to what is shown below.

How can I flatten something like this to remove the top-level list 
structure, i.e.,
return a single-level list of "foo" objects, of class "foolist"?

foo <- function(n) {
     result <- list(x=sample(1:10,n), y=sample(1:10,n))
     class(result) <- "foo"
     result
}

multifoo <- function(vec, label, ...) {
     result <- lapply(vec, foo, ...)
     names(result) <- paste0(label, vec)
     class(result) <- "foolist"
     result
}

foo1 <- multifoo(1:2, "A")
foo2 <- multifoo(1:2, "B")

mfoo <- list(A=foo1, B=foo2)

str(mfoo, 2)

 > str(mfoo, 2)
List of 2
  $ A:List of 2
   ..$ A1:List of 2
   .. ..- attr(*, "class")= chr "foo"
   ..$ A2:List of 2
   .. ..- attr(*, "class")= chr "foo"
   ..- attr(*, "class")= chr "foolist"
  $ B:List of 2
   ..$ B1:List of 2
   .. ..- attr(*, "class")= chr "foo"
   ..$ B2:List of 2
   .. ..- attr(*, "class")= chr "foo"
   ..- attr(*, "class")= chr "foolist"

In this case, what is wanted is a single-level list, of 4 foo objects, 
A1, A2, B1, B2,
all of class "foolist"

-- 
Michael Friendly     Email: friendly AT yorku DOT ca
Professor, Psychology Dept. & Chair, Quantitative Methods
York University      Voice: 416 736-2100 x66249 Fax: 416 736-5814
4700 Keele Street    Web:   http://www.datavis.ca
Toronto, ONT  M3J 1P3 CANADA