R6DS {R6DS}

R6DS: provides reference classes implementing some useful data stuctures.

Description

R6DS stands for R6 class based Data Structures. The package provides reference classes implementing some useful data stuctures.

Details

Some data structures are quite useful in solving some programming problems, as they offer great convenience and are the keys to implement some algorithms.

The package implements these data structures by using the reference class R6. Each class defined in the package represents a certain data structure, and it inherits the R6 reference class which means that it is also a reference class.

In order to create an instance of the R6 type reference class, you will have to use its new method as follows:

instance <- RStack$new()

where RStack is an R6 type reference class.

The reference class has the feature that each time when you pass (or assign) an instance of the reference class to somewhere, it is not pass-by-value but pass-by-reference. For example, suppose there is an instance of the reference class x who has an attribute x$y. If you pass it to a function func by using func(x), the function will not copy x but pass it as a reference. Inside the function func, if there is a sentence like

x$y <- 0

then the attribute y of the global x outside the function will be changed to zero.

Of course you can copy the instance of a reference class, but you have to use its clone method:

new_instance <- instance$clone()

Notice that all the classes in the package use instances of some other R6 type reference class as their members. This implies that, according to the rule of the R6 family, you have to add deep = TRUE when you clone their instances:

new_instance <- instance$clone(deep=TRUE)

and then you can successfully copy them.

The classes in the package are designed in the way that you cannot get the access to their members directly, as they are declared to be private. Instead, you have to use their methods (member functions) to get them. In the following, a complete list of these classes and their methods in common are presented. Each class has its own methods, and for details of these class-specific methods please refer to their help documents.

Some methods are declared to be "active", or active method, which means that, when you call them, you do not need to use parenthesis. For example, the size method is a common active method of all classes in the package. When you call it, you do

instance$size

So it looks pretty like a member attribute, but actually not.

How to Use the Package

All classes in the package are declared to be non-portable and non-class (R6 standards), which means that the user of the package cannot inherit them.

The user can create and use instances of these classes, and the instances can contain any R objects (vector, matrix, factor, data.frame, list and etc.) as their values.

The author suggest that the user of the package puts the instances of these classes inside other classes to be their members.

But it is still possible to inherit the classes in the package. To this end, the user can copy and paste the source code of the package.

Author and Maintainer

Yukai Yang

Department of Statistics, Uppsala University

[e-mail]

References

For the details about the data structures, see Data Structure at Wikipedia.

Classes Available in the Package

RStack The RStack reference class implements the data structure stack.

RQueue The RQueue reference class implements the data structure queue.

RDeque The RDeque reference class implements the data structure double-ended queue.

RDLL The RDLL reference class implements the data structure doubly linked list.

RSet The RSet reference class implements the data structure set.

RDict The RDict reference class implements the data structure dictionary.

RBST The RBST reference class implements the data structure binary search tree.

Common Methods of the Classes in the Package

new(..., collapse=NULL)

a method belonging to the class which create an instance of the class. The method creates a new instance of some class in the package containing the values in ... and collapse as its elements.

toList

an active immutable method of an instance which returns a list containing its elements (a copy).

Note that RBST has multiple versions of the toList methods.

is_empty()

a method which returns a boolean showing if the instance is empty.

size

an active immutable method of an instance to return its size (like the length of an R vector).

release()

a method of an instance which does the garbage collection and releases the redundant memory occupation.

Note that RDict RBST do not have this methhod.