Click here to see.
Why use R6?
Check to see if the package is there
if (!require('R6')){
install.packages("R6")
}else
{
require('R6')
}Optional Code: if the user wants to download the document as a pdf
if(!file.exists('R6 Documentation')){
download.file('https://cran.r-project.org/web/packages/R6/R6.pdf','R6 Documentation',mode = 'wb')
}Learning by running the functions from the document
class_generator <- R6Class()
object <- class_generator$new()
is.R6Class(class_generator)[1] TRUE
is.R6(class_generator)[1] FALSE
is.R6Class(object)[1] FALSE
is.R6(object)[1] TRUE From Hadley Wickham’s Advanced R
R6 objects have reference semantics which means that they are modified in-place, not copied-on-modify.
Modified in place means the object value is changed then and there, no copying of object and then changing the value of the copied object
Which means you lose what was inside of the original object
Saves memory
Before learning this let’s look at an example explained in Advanced R. A little side note to runif. Before today I used to speak it as run-if. Although I knew its functionality I never captured the idea that it is actually r-unif which is uniform distribution in R.Silly me
x <- data.frame(matrix(runif(5 * 1e4), ncol = 5))
medians <- vapply(x, median, numeric(1))
for (i in seq_along(medians)) {
x[[i]] <- x[[i]] - medians[[i]]
}Below is the code which shows how many times a object has been created.
for (i in 1:5) {
x[[i]] <- x[[i]] - medians[[i]]
}Accumulator<-R6Class("Accumulator",list(
sum=0,
add=function(x=1){
self$sum<-self$sum+x
invisible(self)
}
))# Creating an object from the class
x<-Accumulator$new()
x$add(1)
x$add(4)
x$sum[1] 5
The output of the above code would be 5 instead of 4 because the object replaces the sum or overwrites it.
Method Chaining: x\(add(2)\)add(6)
The below code would throw an error since a non-numeric argument was passed to the function
# x$add('two')$sum
# Initialization method
Person<-R6Class("Person",list(
name=NULL,
age=NA,
initialize=function(name,age){
stopifnot(is.character(name),length(name)==1)
stopifnot(is.numeric(age),length(age)==1)
self$name<-name
self$age<-age
}
))
aadish<-Person$new("Aadish",age=38)
aadish$age[1] 38
aadish$name[1] “Aadish”
#Print method
Person<-R6Class("Person",list(
name=NULL,
age=NA,
initialize=function(name,age){
stopifnot(is.character(name),length(name)==1)
stopifnot(is.numeric(age),length(age)==1)
self$name<-name
self$age<-age
},
print=function(...){
cat("Person: \n")
cat(" Name ",self$name,"\n",sep="")
cat(" Age: ",self$age,"\n",sep="")
}
))
aadish2<-Person$new("Aadish",74)
aadish2Person: Name Aadish Age: 74
AccumulatorChatty<-R6Class("Accumulator Chatty",
inherit=Accumulator,
public=list(
add=function(x=1){
cat("Adding ",x,"\n",sep=" ")
super$add(x=x)
}
))In this example we learnt that we can inherit all the members( fields and methods) of the parent class. The add method invokes the add function from the parent class , a concept which is there in JAVA (Yes, I know JAVA only).
When Accumulator Chatty is run since it has it’s own add class it will overide the parent class but we can use some functionalities like the ADDING operation from the parent class
AccumulatorChatty_obj<-AccumulatorChatty$new()
AccumulatorChatty_obj$add(10)$add(20)$sumAdding 10 Adding 20 [1] 30
I want to build an accumulator without using an R6 class
These exercises are part of Hadley’s book
BankAccount<-R6Class("BankAccount",list(
balance=0,
deposit=function(amount){
self$balance=self$balance+amount
invisible(self)
},
withdraw=function(amount){
self$balance=self$balance-amount
invisible(self)
}
))
BankAccountobj<-BankAccount$new()
BankAccountobj$deposit(20)
BankAccountobj$deposit(100)
BankAccountobj$withdraw(10)
BankAccountobj$balance[1] 110
BankAccountOverdraft<-R6Class("BankAccountOverdraft",
inherit =BankAccount,
list(
withdraw=function(amount){
cat('your balance is',self$balance,"\n")
if(amount < self$balance){
super$withdraw(amount)
}else
{
print("Withdrawal amount more than balance")
}
}
))
BankAccountOverdraftobj<-BankAccountOverdraft$new()
BankAccountOverdraftobj$deposit(20)
BankAccountOverdraftobj$withdraw(40)your balance is 20 [1] “Withdrawal amount more than balance”
BankAccountOverdraftobj$balance[1] 20
BankAccountOverdraftFees<-R6Class("BankAccountOverdraftFees",
inherit =BankAccount,
list(
Fees=0,withdraw=function(amount){
if(amount < self$balance){
super$withdraw(amount)
}else
{
self$Fees=(amount-self$balance)*0.035
super$withdraw(amount)
cat("Withdrawal amount more than balance",'Fees charged $',self$Fees)
}
}
))
BankAccountOverdraftFeesobj<-BankAccountOverdraftFees$new()
BankAccountOverdraftFeesobj$deposit(20)
BankAccountOverdraftFeesobj$deposit(40)
BankAccountOverdraftFeesobj$withdraw(40)
BankAccountOverdraftFeesobj$balance[1] 20
Creating the cards
suit <- c("♠", "♥", "♦", "♣")
value <- c("A", 2:10, "J", "Q", "K")
cards <- paste0(rep(value, 4), suit)Defining a R6 class
Question 2 Solution Part 1
DeckCards<-R6Class("DeckCards",list(
suit = c("♠", "♥", "♦", "♣"),
value = c("A", 2:10, "J", "Q", "K"),
cards = paste0(rep(value, 4), suit),
picked=0,
# min=0,
# max=0,
# number=0,
draw=function(number=1){
self$picked=sample(self$cards,number,replace=F)
cat('your picked card is',self$picked," ")
self$cards<-self$cards[!self$cards %in% self$picked]
invisible(self)
},
reshuffle=function(){
self$cards<-cards
}
))
DeckCards<-DeckCards$new()
DeckCards$cards[1] “A
DeckCards$draw()your picked card is 8
DeckCards$draw()your picked card is 10
You can add an if-else statement to the draw function which checks the lenght of the cards.Because in this case after 52 attempts size of cards would be zero and the function would throw an error.
Controlling access: Private and active fields.
Person <- R6Class("Person",
public = list(
initialize = function(name, age = NA) {
private$name <- name
private$age <- age
},
print = function(...) {
cat("Person: \n")
cat(" Name: ", private$name, "\n", sep = "")
cat(" Age: ", private$age, "\n", sep = "")
}
),
private = list(
age = NA,
name = NULL
)
)Differences. Looking at the code we can see that the variables name, age are declared outside of the public. If you want to access these variables you have to use private$
You can not access them by using private $name or private $age. Example would be you don’t want to show marks but only pass or fail, or if a person has cancer or not but not their vitals.