StateStack

Introduction

An R package implementing a push pop stack which allows for reading and writing to the top value of the stack. An example of a use for this class would be to store a series of states while traversing a tree structure.

The stack will be created with a single element in the stack to be used as the current state, this value can be specified in the constructor or if undefined will default to 0. As such starting $depth() is 1 and cannot be reduced beneath 1.

StateStack has the following functions: $push(), $pop(), $peek(), $set(), $depth() and $clear(). It also has an active binding called $state which can be used to read or write to the current state (equivalent to using $peek() and $set().)

Calling $pop() more times than $push() will throw an error.

$push() : Will push the supplied value to the top of the stack. If no value is supplied will copy the current state.

$pop() : Will pop the current state from the stack and return it.

$peek(): Will return the current state from the stack without removing it.

$set() : Will change the current state without changing the stack

$depth(): Will return the number of layers in the stack.

$clear(): Will clear the stack making the current state the supplied value.

Utilisation

library(statestackr)

#instantiate a new state Stack with a starting value of 7L
statestack <- StateStack$new(7L)

#check the current state
statestack$state
#> [1] 7
statestack$depth()
#> [1] 1

#Update the current state
statestack$state <- 2L
statestack$state
#> [1] 2
statestack$depth()
#> [1] 1

#Store the old state and make a new current state.
#Not supplying an argument will copy the current state and push it onto the stack.
#Changing the current state will not affect the first state on the stack.
statestack$push()
statestack$state
#> [1] 2
statestack$depth()
#> [1] 2

#Update the current state
statestack$state <- 3L
statestack$state
#> [1] 3
statestack$depth()
#> [1] 2

#Update the current state
statestack$state <- 1L
statestack$state
#> [1] 1
statestack$depth()
#> [1] 2

#Remove the top item of the stack and return it
statestack$pop()
#> [1] 1
statestack$depth()
#> [1] 1

#Check that the state stored before the previous push() has been retained
statestack$state
#> [1] 2
statestack$depth()
#> [1] 1

Installation

To install from GitHub

# install.packages("devtools")
devtools::install_github("Thormidable/statestackr")

Contribution

Please report any issues.

Pull requests are always welcome.

Documentation

• R6 class package