[R] Stack type

[Duncan Murdoch]

On 01/03/2010 7:56 PM, Worik R wrote:
> How can I implement a stack in R?
> 
> I want to push and pop.  Every thing I push and pop will be the same
> type, but not necessarily an atomic type.

Use lexical scoping:

stack <- function() {
   store <- list()
   push <- function(item) {
     store <<- c(list(item), store)
     invisible(length(store))
   }
   pop <- function() {
     if (!length(store)) stop("Nothing to pop!")
     result <- store[[1]]
     store[[1]] <<- NULL
     result
   }
   list(push=push, pop=pop)
}

mystack <- stack()
mystack$push( 1 )
mystack$push( letters )
mystack$pop()
mystack$pop()
mystack$pop() # gives an error

Duncan Murdoch