4 messages · David Forrest, Marc Schwartz, Barry Rowlingson
Is there a package for stacks with pushing and popping? I'd really like to do something like push(par(no.readonly=TRUE)) some stuff.... par(pop()) It seems like it wouldn't be difficult, and that someone may have already implemented a set of stack functions, and I wouldn't like to duplicate it. Thanks for your time, Dave
Dave Forrest (434)924-3954w(111B) (804)642-0662h (804)695-2026p drf5n at virginia.edu http://mug.sys.virginia.edu/~drf5n/
-----Original Message----- From: r-help-admin at stat.math.ethz.ch [mailto:r-help-admin at stat.math.ethz.ch] On Behalf Of David Forrest Sent: Tuesday, February 25, 2003 11:34 AM To: r-help at stat.math.ethz.ch Subject: [R] push/pop on a stack Is there a package for stacks with pushing and popping? I'd really like to do something like push(par(no.readonly=TRUE)) some stuff.... par(pop()) It seems like it wouldn't be difficult, and that someone may have already implemented a set of stack functions, and I wouldn't like to duplicate it. Thanks for your time, Dave
In at least that particular example, the same save/restore operation can be achieved by: old.pars <- par(no.readonly=TRUE) ...other code par(old.pars) That is in the examples in ?par. Not sure that you need a LIFO based stack mechanism for that unless I am missing something. HTH, Marc Schwartz
It seems like it wouldn't be difficult, and that someone may have already implemented a set of stack functions, and I wouldn't like to duplicate it.
Here's a Tuesday evening lash-up. Usage is:
> mystack <- stack() # initialisation
> push(mystack,value) # stores something on the stack
> pop(mystack) # returns 'value'
There's a print method that lists the stack. Its simply a list. Stack
underflow is reported as 'attempt to select less than one element'. You
can push anything on the stack. Almost. I just tried pushing a stack
object onto the stack, and got infinite recursion, cant think why.
Anyway, this seems to work for most sensible situations!
stack <- function(){
it <- list()
res <- list(
push=function(x){
it[[length(it)+1]] <<- x
},
pop=function(){
val <- it[[length(it)]]
it <<- it[-length(it)]
return(val)
},
value=function(){
return(it)
}
)
class(res) <- "stack"
res
}
print.stack <- function(x,...){
print(x$value())
}
push <- function(stack,obj){
stack$push(obj)
}
pop <- function(stack){
stack$pop()
}
Baz
-----Original Message----- From: r-help-admin at stat.math.ethz.ch [mailto:r-help-admin at stat.math.ethz.ch] On Behalf Of Barry Rowlingson Sent: Tuesday, February 25, 2003 12:10 PM To: David Forrest Cc: r-help at stat.math.ethz.ch Subject: Re: [R] push/pop on a stack
It seems like it wouldn't be difficult, and that someone may have already implemented a set of stack functions, and I wouldn't like
to
duplicate it.
Here's a Tuesday evening lash-up. Usage is:
> mystack <- stack() # initialisation > push(mystack,value) # stores something on the stack > pop(mystack) # returns 'value'
There's a print method that lists the stack. Its simply a list. Stack
underflow is reported as 'attempt to select less than one
element'. You
can push anything on the stack. Almost. I just tried pushing a stack
object onto the stack, and got infinite recursion, cant think why.
Anyway, this seems to work for most sensible situations!
stack <- function(){
it <- list()
res <- list(
push=function(x){
it[[length(it)+1]] <<- x
},
pop=function(){
val <- it[[length(it)]]
it <<- it[-length(it)]
return(val)
},
value=function(){
return(it)
}
)
class(res) <- "stack"
res
}
print.stack <- function(x,...){
print(x$value())
}
push <- function(stack,obj){
stack$push(obj)
}
pop <- function(stack){
stack$pop()
}
Baz
Just as an FYI, if you should elect to implement that function, there is already a stack() function in base R, so you would want to use a different name. See ?stack, which is used to transform data. Regards, Marc