Raw Message

Message-ID: <971536df1003020533g202b36a9p4126d3af34194a3c@mail.gmail.com>
Date: 2010-03-02T13:33:43Z
From: Gabor Grothendieck
Subject: Stack type
In-Reply-To: <4B8C666C.9070002@stats.uwo.ca>

Here is an example using proto based on converting Duncan's example:

library(proto)
Stack <- proto(new = function(.) proto(Stack,
	stack = NULL,
	push = function(., el) .$stack <- c(list(el), .$stack),
	pop = function(.) { stopifnot(length(.$stack) > 0)
		out <- .$stack[[1]]
		.$stack[[1]] <- NULL
		out
	}))

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


On Mon, Mar 1, 2010 at 8:14 PM, Duncan Murdoch <murdoch at stats.uwo.ca> wrote:
> 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
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>