R6DS (version 1.2.0)

RStack: The RStack reference class

Description

The RStack reference class implements the data structure stack.

Usage

RStack

Format

An object of class R6ClassGenerator of length 24.

Immutable Methods

The immutable method does not change the instance.

peek()

This method returns the last pushed (top or rightmost) element in the stack. It returns NULL if the stack is empty.

Mutable Methods

The mutable methods change the instance.

push(..., collapse=NULL)

The push method pushes the elements in ... and collapse into the stack (to the top or right).

Note that you can input multiple elements.

pop()

The pop method pops (returns and removes) the last pushed (rightmost) element in the stack. It returns NULL if the stack is empty.

Details

A stack is an ordered list of elements following the Last-In-First-Out (LIFO) principle. The push method takes elements and add them to the top position (right) of the stack, while the pop method returns and removes the last "pushed" (top or rightmost) element in the stack.

The elements in the stack are not necessarily to be of the same type, and they can be any R objects.

References

For the details about the stack data structure, see Stack at Wikipedia.

See Also

R6DS for the introduction of the reference class and some common methods

Examples

# NOT RUN {
### create a new instance

# to create a new instance of the class
stack <- RStack$new()

# the previous RStack instance will be removed if you run
stack <- RStack$new(0, 1, 2, collapse=list(3, 4))
# the following sentence is equivalent to the above
stack <- RStack$new(0, 1, 2, 3, 4)
# where the numbers 0, 1, 2, 3, 4 are pushed into the stack

### push elements

# it can be one single element
stack$push(5)
# it can be several elements separated by commas
# note the whole list will be one element of the stack
# because it is not passed through the collapse argument
stack$push(list(a=10,b=20), "Hello world!")
# the collapse argument takes a list whose elements will be collapsed
# but the elements' names will not be saved
stack$push(collapse = list(x=100,y=200))
# they can be used together
stack$push("hurrah", collapse = list("RStack",300))

### pop an element

# pop only one element at a time
val <- stack$pop()
# then we keep poping!
while(!is.null(val)) val <- stack$pop()

# }