Simplify the Structure of a List
DESCRIPTION:
Returns a vector or a list which is the result of simplifying the recursive structure of the input list.
USAGE: 
unlist(data, recursive=T, use.names=T)
REQUIRED ARGUMENTS:
data:
any S-PLUS object, generally a list.
OPTIONAL ARGUMENTS:
recursive:
logical flag: should unlisting be done recursively?
use.names:
logical flag: should the computations create a names attribute for the resulting object, using the component names (possibly at several levels) of data? If FALSE, the resulting object will not have a names attribute. If TRUE, the function will use the rule below to construct a names attribute for the result.
VALUE:
a vector (or list) created by combining (see c) the components of data. If recursive is TRUE, each component of data is unlisted (with recursive=TRUE) before it is combined. Thinking of data as a tree, the effect of unlist with recursive=T is to produce a vector of all the leaves. The mode of the result is the most general of all the modes of the components of data, or of the leaves of data if recursive is TRUE.
DETAILS:
If use.names is TRUE, names are built from the component names according to the following rules: Suppose x is a component of data and xname represents its corresponding name; then, in the unlisted version, x has names which are made by pasting xname and the names attribute of x, with separator "." (assuming that both strings are non-empty). If xname is the empty string (i.e., x has no component name) just the names attribute of x is used, if any. If xname is non-empty but x has no names attribute, then xname is used followed by the index of the corresponding element in x (no separating "." in this case). If x has length 1, the redundant "1" is not pasted on.

If recursive is TRUE, the rule above is applied, bottom up, recursively. The same rule applies to names created by the c() function, with the equivalence shown below. The algorithm does not enforce rules on the names, such as uniqueness or that every name be non-empty. Use names(x) <- make.names(names(x), unique=T) to enforce such rules.

c(..., recursive=T) is equivalent to unlist(list(...), recursive=T).

This is a generic function; there are currently no methods for it.

SEE ALSO:
c , list .
EXAMPLES: 
lista <- list(1:3, a=5:7, b=list(b1=12:14, b2=c(23, 25, 28)))
unlist(lista) # a vector of length 12
unlist(lista, recursive=F)
# a list of length 8 with final components b.b1 and b.b2
# equivalent to list(1, 2, 3, a1=5, a2=6, a3=7, b.b1=12:14, b.b2=c(23,25,28))


# build a vector of variable-length results where fun returns a list
x <- vector("list", n)
for(i in 1:n)
  x[[i]] <- fun(i)
x <- unlist(x, recursive=F)


x <- list(A=1,B=c(a=2,b=3,4),list(d=5,6))  # names construction
unlist(x)
  A B.a B.b B3 d
  1   2   3  4 5 6